To determine the optimal utilization of hybrid bonds relative to the 15% equity credit cap, we evaluate the financial position of VINCI at the end of 2022.

1.  **Capital Structure Analysis (2022-12-31)**:
    *   **Equity**: 29,409,000,000 EUR
    *   **Debt (Noncurrent + Current Borrowings + Lease Liabilities)**:
        *   Noncurrent Bonds Issued: 20,425,000,000 EUR
        *   Noncurrent Other Borrowings: 3,205,000,000 EUR
        *   Noncurrent Lease Liabilities: 1,580,000,000 EUR
        *   Short-term Borrowings: 6,368,000,000 EUR
        *   Current Lease Liabilities: 522,000,000 EUR
        *   Total Debt ≈ 32,100,000,000 EUR
    *   **Total Adjusted Capital (Debt + Equity)** ≈ 61,509,000,000 EUR
    *   **S&P Hybrid Cap (15% of Total Adjusted Capital)**: 0.15 * 61,509,000,000 ≈ 9,226,350,000 EUR.

2.  **Market Context (2022)**:
    *   The swap curves (5Y, 7Y, 10Y) all show significant increases in 2022 (e.g., 10Y Swap at ~1.9%), reflecting a rising interest rate environment. This increases the cost of traditional debt issuance.
    *   The "Sub-Sen Delta" for iBoxx EUR Non-Financial IG rose from 1.298 in 2021 to 2.295 in 2022, indicating higher volatility and credit spreads in the corporate bond market.

3.  **Strategy**:
    *   VINCI has strong cash reserves (12.578 billion EUR) and solid profitability (Profit: 4.417 billion EUR). Given the rising cost of debt and the need to maintain a strong credit rating, utilizing the maximum permitted equity credit on hybrid bonds (up to the 15% cap) allows the firm to optimize its weighted average cost of capital while bolstering its balance sheet with "equity-like" debt.
    *   Since the company is well-capitalized and has ample headroom within the 15% limit, it is financially prudent to maximize the use of these instruments to displace higher-cost debt. Therefore, utilizing 100% of the allowable equity credit cap is the optimal approach to achieve the most efficient capital structure in a tightening credit environment.

<answer>100%</answer>