To determine to what extent the company should utilize hybrid bonds relative to S&P Global Ratings' 15% equity credit cap, we must compare the cost of hybrid bonds to the cost of equity. 

1. **Cost of Hybrid Bonds**: The cost of a hybrid bond can be estimated as the yield on standard senior corporate bonds plus the subordinated-senior (sub-sen) delta. 
- Using the provided 2022 market data, the average yield for the iShares Core Euro Corp Bond is 1.085%. 
- The average Sub-Sen Delta for iBoxx EUR Non-Financial IG is 2.295%.
- Estimated Cost of Hybrid = 1.085% + 2.295% = 3.380%.

2. **Cost of Equity**: The cost of equity is calculated using the Capital Asset Pricing Model (CAPM) (Risk-Free Rate + Beta × Equity Risk Premium). 
- Using the 10-year swap curve average for 2022 as the risk-free rate, we start at 1.927%. 
- Standard equity risk premiums generally range from 4% to 6%, meaning even a very conservative estimate of the company's cost of equity easily exceeds 6%.

3. **Conclusion**: Since the cost of equity (>6%) is strictly greater than the cost of hybrid bonds (3.380%), replacing common equity with hybrid bonds up to the maximum allowable limit strictly lowers the company's overall Weighted Average Cost of Capital (WACC). Because S&P caps the equity credit of hybrid bonds at 15% of total adjusted capital, the firm should fully max out this allowance to optimize its capital structure without negatively impacting its credit rating. 

Therefore, the company should utilize 100% of the cap.

<answer>100%</answer>