Based on the provided 2022 IFRS financials, Italgas S.p.A. appears to have sizable leverage and a mature regulated utility profile, with elevated long-term debt and substantial noncurrent liabilities. Notable points:

- Equity attributable to owners of parent: 2,108,262,000 EUR (2023) vs. total equity 2,390,570,000 EUR; affordable but light relative to gross debt.
- Liabilities total: 8,639,987,000 EUR (2023), with long-term financial liabilities excluding other non-current: 6,402,913,000 EUR (2023). This implies high leverage.
- Current assets declined year-over-year, while current liabilities roughly stable, signaling potentially tighter working capital but not catastrophic.
- Cash and cash equivalents collapsed from 1,391,763,000 (2022-01-01) to 451,946,000 (2023-01-01), suggesting tighter liquidity in 2023; 2022 numbers show good liquidity but 2023 position is tighter, possibly presaging refinancing needs.
- Hybrid instruments (per problem, started absence of current hybrids) are not listed; assume position as of 2022 base.

Rating methodology for Regulated Utilities indicates that hybrids are often used to improve leverage metrics and maintain regulatory funding flexibility. Given Italgas’ high long-term debt and potential capex needs from regulated infrastructure, but with a strong regulatory framework and stable cash flows, hybrids could provide modest uplift to equity credit and preserve rating. However, the problem asks to choose a percentage up to 15% of total adjusted capital, considering a max annual issuance of 3b EUR.

From the numbers:
- Total adjusted capital = Equity + Adjusted Debt. Rough estimate: Equity around 2.39b as of 2023; debt around long-term financial liabilities 6.40b plus short-term financial liabilities 1.42b = 7.82b; plus other components. Adjusted capital could be around 10-11b. Hybrid capacity cap at 15% would be around 1.5-1.7b. Starting point: hybrid outstanding not given; assume none or minimal.

Credit considerations: 2022-2023, rising interest costs, but swaps and cost of debt; If hybrid cost is higher than debt but improves equity ratio, modest use could be beneficial.

The guidelines indicate:
- If high capex intensity and large acquisition pipeline with leverage pressure, 11.25% or 15% may be warranted.
- If moderate needs with headroom, 7.5% or 3.75%.

Italgas has high regulated framework and relatively stable cash flows; refinancing needs exist due to high long-term debt; however, the 2023 liquidity reduction suggests some refinancing pressure but not an immediate crisis. Capex needs in regulated networks tend to be predictable; ratio optimization could help.

Therefore, I would recommend a mid-range, i.e., 7.5% of total adjusted capital, balancing moderate leverage optimization and rating headroom, with potential to step up to 11.25% if refinancing pressure accelerates or capex/investment pipeline expands.

Final answer: 7.5%