Let’s break this down.  

**1. Business & financial snapshot**  
- ENGIE is a large European utility with a mix of regulated networks, renewables, and some merchant exposure.  
- In 2022, revenue nearly doubled, but operating income fell sharply, with a **net loss from continuing operations** of -€1.793bn. Profit only turned positive due to discontinued operations.  
- S&P metrics: Net Debt/EBITDA = **3.25x**, FFO/Net Debt = **24.8%** — this is solidly investment-grade but not “A range” strongly.  
- Moody’s says adjusted leverage trend is **improving**.  

**2. Existing hybrid position**  
- ENGIE already has deeply subordinated perpetual notes in its equity structure: €3.767bn at end-2021, €3.393bn at end-2022.  
- It has been issuing hybrids since 2014, and did so in 2021/2022 (evidenced by the “Operations on Deeply Subordinated Perpetual Notes” lines).  
- This tells us hybrids are a regular part of their capital management, not a one-off.  

**3. Rationale for more hybrids**  
- Large capex needs (over €6bn in investing activities, plus net investments in growth/renewables).  
- Refinancing activity remains significant (borrowings/repayments of several billions).  
- Hybrids help keep adjusted leverage metrics comfortable, especially important when earnings are under pressure from non-cash items (fair value losses, impairments).  
- Interest rate environment: 2022 swap rates jumped to ~1.7–1.9%, but the subordinated spread for IG non-financials was ~2.3% avg — still manageable for a large utility.  
- Regulatory advantage for ENGIE is likely “strong/adequate” given French and EU frameworks, which supports the stability needed to service hybrids.  

**4. What percentage is advisable?**  
- Total adjusted capital is roughly €39bn equity + adjusted debt, so 15% cap is ~€5.9bn.  
- Existing hybrids are already ~€3.4bn, which is **~8.7%** of adjusted capital.  
- Issuing up to 11.25% (adding ~€1bn more) or 15% (adding ~€2.5bn more) would still be within their historical cap and issuance pace (<€3bn/year limit).  
- However, 15% would mean maxing out the S&P equity credit cap, which is aggressive and typically reserved for transformational capex/M&A or severe downgrade risk — not the case here.  
- 11.25% fits better: big ongoing spending, moderate rating headroom benefits, and historically they’ve used hybrids actively but not to the absolute limit.  

**Conclusion**: Given past behavior, moderate leverage pressure, and ongoing investment needs, moving toward the upper end but not the absolute max is reasonable.  

<answer>11.25%</answer>