Let’s reason through this step-by-step.  

**1. Nature of the company and cash flow stability**  
VERBUND AG is an Austrian utility with the bulk of its revenue coming from electricity sales and grid operations. Utilities generally have relatively stable cash flows, though these can be influenced by energy prices, as seen in the jump in revenue from 2021 to 2022.  

**2. Profitability and coverage**  
In 2022, EBITDA jumped to €3.16 billion and net profit nearly doubled. Interest expense was just €101.7 million, so the interest coverage ratio (EBITDA/interest) is very high (~31x). This suggests ample capacity to service additional debt, including hybrids.  

**3. Leverage and equity cushion**  
Equity at end-2022 was €8.32 billion, while noncurrent financial liabilities were €2.84 billion and current financial liabilities €1.11 billion. Total debt is moderate relative to equity, and hybrid issuance would not immediately threaten credit metrics.  

**4. Cost of hybrid debt**  
Given rising rates (the 5Y swap went from negative to 1.726% average in 2022, and corporate bond yields also increased), hybrid debt is more expensive than in the past. However, for a strong IG company, the after-tax cost may still be attractive relative to equity.  

**5. S&P’s 15% cap**  
The 15% cap is on hybrid equity credit *as a share of total adjusted capital*. If we estimate total adjusted capital at ~€11–12 billion, the limit would be around €1.7–1.8 billion. The company has room within that cap.  

**6. Strategic use of hybrids**  
Given the company’s high profitability, low leverage, and the need to fund investments (CapEx was ~€1.09 billion in 2022), some use of hybrids makes sense to optimize the capital structure without excessively diluting equity or relying solely on senior debt. However, going to 100% of the cap may be unnecessary and costly. A moderate approach, like 50–75%, would balance cost efficiency and rating headroom, but given interest rate trends, a more cautious 50% utilization is plausible.  

I’ll conclude with **50%**.

<answer>50%</answer>