To determine the optimal extent to which Bouygues should utilize hybrid bonds relative to the S&P Global Ratings cap, we must analyze the company's current capital structure, credit profile, and the mechanical impact of hybrid debt on its rating metrics.

**1. Calculate Current Capital Structure and Leverage:**

First, we extract the relevant balance sheet figures for the end of 2022 (2023-01-01 data point in the report):
*   **Total Equity:** 13,932 million EUR
*   **Total Assets:** 60,595 million EUR
*   **Total Liabilities:** Assets - Equity = 60,595 - 13,932 = 46,663 million EUR
*   **Net Debt:** 7,440 million EUR (provided directly)
*   **Gross Debt:** We can approximate gross debt or use Net Debt for leverage ratios. S&P typically uses Gross Debt for capitalization calculations but Net Debt for leverage coverage. Let's look at the "Total Adjusted Capital" definition provided: Debt + Equity.
    *   Using Net Debt as a proxy for the debt burden relevant to equity credit calculations (since cash offsets debt):
    *   Total Adjusted Capital (using Net Debt) = Net Debt + Equity = 7,440 + 13,932 = 21,372 million EUR.
    *   Alternatively, using Gross Debt components: Long-term borrowings (11,586) + Current borrowings (1,361) + Lease Liabilities (2,107 + 498) + Overdrafts (418) ≈ 15,970 million EUR.
    *   Total Adjusted Capital (using Gross Debt) = 15,970 + 13,932 = 29,902 million EUR.

Let's look at the leverage ratio (Debt / (Debt + Equity)):
*   Using Gross Debt: 15,970 / 29,902 ≈ 53.4%
*   Using Net Debt: 7,440 / 21,372 ≈ 34.8%

Bouygues is a large, diversified conglomerate (Construction, Media/TF1, Telecom/Orange stake). Its credit profile is generally investment grade. S&P Global Ratings typically assigns an 'A' or 'BBB+' range to such entities depending on leverage.

**2. Analyze the Hybrid Bond Mechanism:**

S&P Global Ratings grants "equity credit" to hybrid bonds, treating a portion of the hybrid instrument as equity rather than debt for rating purposes.
*   **Standard Equity Credit:** Typically 50% for strong issuers, potentially up to 100% for very strong issuers with specific features, but often capped or reduced if leverage is high.
*   **The Cap:** The prompt specifies a cap where equity credit is limited to a maximum of 15% of total adjusted capital. This implies that the *amount of hybrid debt treated as equity* cannot exceed 15% of the total capital base.

**3. Determine the Strategic Need for Hybrids:**

*   **Credit Rating Optimization:** Companies issue hybrids to lower their reported leverage ratios (Debt/EBITDA or Debt/Capital) to maintain or improve their credit rating. By treating hybrids as equity, the denominator (Capital) increases with equity-like treatment, and the numerator (Debt) decreases (partially or fully).
*   **Current Leverage:** Bouygues' net debt/EBITDA is a key metric.
    *   EBITDA (approx): Profit from Operating Activities (1,872) + Depreciation/Amortization (2,228) + Impairment/Provisions (172) ≈ 4,272 million EUR.
    *   Net Debt / EBITDA = 7,440 / 4,272 ≈ 1.74x.
    *   This is a very healthy leverage ratio for an industrial conglomerate. An ratio of < 2.0x is typically consistent with an 'A' rating or higher.
*   **Cost of Capital:** Hybrid bonds carry a higher coupon than senior debt because they are subordinated and have equity-like risk. If the company already has a strong credit profile (low leverage), issuing expensive hybrid debt to gain marginal equity credit is inefficient. The "equity credit" benefit is most valuable when a company is near a rating threshold (e.g., BBB+ to A-) and needs to artificially lower leverage to avoid a downgrade or achieve an upgrade.
*   **Market Conditions (2022):** The swap curves and bond spreads show a significant increase in rates in 2022 compared to 2020-2021.
    *   10Y Swap Average: 1.927% (up from 0.053% in 2021).
    *   iBoxx EUR Non-Financial IG Spread: 2.295% (up from 1.298% in 2021).
    *   The cost of issuing any debt, especially subordinated hybrid debt (which would include a spread over swaps + credit spread + illiquidity premium), is significantly higher in 2022.

**4. Evaluating the Options:**

*   **100% Utilization:** This would mean issuing enough hybrids to hit the 15% equity credit cap. This increases interest expenses significantly without a pressing need to repair the balance sheet, given the low 1.74x Net Debt/EBITDA. It is capital inefficient.
*   **75% / 50% Utilization:** Still implies a significant issuance of costly capital.
*   **25% Utilization:** A moderate approach, but still incurs higher costs than senior debt.
*   **0% Utilization:** Given the strong existing equity base (Equity/Assets ≈ 23%), low net leverage, and the high cost of capital in 2022, there is no immediate financial distress or rating pressure requiring the engineering of capital via hybrids. The company can fund operations and investments through retained earnings, senior debt, or existing cash flows more cheaply. Furthermore, hybrids are complex instruments; if not needed for rating optimization, they add unnecessary complexity and cost.

However, we must consider if "utilize relative to cap" implies a strategic target. Many investment-grade industrials maintain a small portion of hybrids to diversify funding sources. But the question asks "To what extent *should* this company utilize...".

Let's look closer at the "Cap" logic. If the cap is 15% of total adjusted capital, and the company has no hybrids, it has 0% utilization. If it issues hybrids, it gains equity credit.
S&P's methodology often allows up to 15% of capital to be treated as equity from hybrids for 'A' rated companies.
Bouygues' leverage is low. The primary driver for hybrids is rating management. With Net Debt/EBITDA at ~1.7x, Bouygues is likely already in a comfortable rating zone. Issuing hybrids would increase the interest burden (Hybrid coupons are often deferrable but accumulate, and are tax-deductible but expensive).

In a rising rate environment (2022 data shows sharp rate hikes), locking in high-cost subordinated debt is unattractive. The "Bear" case for rates is high, meaning costs are high. The "Bull" case is lower, but still much higher than 2021.

Therefore, the prudent financial management decision, absent a specific need to boost equity for a major acquisition that would spike leverage, is to avoid the higher cost of hybrids. The company has sufficient organic equity and access to senior markets.

However, there is a nuance. Does the question imply a *target* capital structure policy? Many large caps target a specific hybrid ratio. But without explicit guidance that Bouygues *needs* to upgrade its rating, the cost-benefit analysis favors 0% or very low utilization.

Let's re-read the prompt's constraint: "limits the equity credit on hybrids to a maximum of 15% of total adjusted capital".
If the company *were* to use hybrids, how much *should* it use?
Usually, if a company decides to use hybrids, it maximizes the benefit up to the cap if it is leverage-constrained. If it is *not* leverage-constrained, it uses 0%.

Is Bouygues leverage constrained?
Net Debt: 7.4B. EBITDA: ~4.3B. Ratio: 1.7x.
Peer comparison: Most European industrials target 2.0x - 2.5x for BBB/A ratings. Bouygues is *below* typical leverage targets. It has "headroom".
Therefore, it does *not* need the equity credit to maintain its rating.
Consequently, it should not incur the higher cost of hybrids.

Thus, the optimal utilization is 0%.

<answer>0%</answer>