To assess the appropriate level of hybrid bond issuance for Bouygues SA, we analyze the financial data for the fiscal year ended December 31, 2022.

**1. Financial Health and Leverage Analysis:**
*   **Net Debt:** As of year-end 2022, Bouygues reported a Net Debt of 7,440 million EUR, a significant increase from 941 million EUR in 2021.
*   **Equity:** Total Equity is 13,932 million EUR.
*   **Total Adjusted Capital:** Using the sum of Equity and Net Debt (as a proxy for adjusted debt), we arrive at approximately 21,372 million EUR.
*   **Liquidity and Debt Profile:** Long-term borrowings increased sharply from 5,805 million EUR in 2021 to 11,586 million EUR in 2022. This substantial increase in leverage is driven by significant acquisition activities (notably the acquisition of Equans, evidenced by the 6,269 million EUR in cash flows used for obtaining control of subsidiaries).

**2. Strategic Context:**
*   Bouygues has undergone a major transformational acquisition (Equans) that has significantly altered its capital structure and increased its debt burden.
*   The rise in net debt and the integration of a large entity typically put pressure on credit metrics. While the operating performance (Revenue of 44.3 billion EUR) remains strong, the jump in leverage indicates that the group is in a phase of significant integration and capital deployment.
*   The interest rate environment (Swap curves) has risen sharply between 2021 and 2022 (e.g., the 10Y Swap moved from 0.053% to 1.927%), increasing the cost of standard debt. Hybrid instruments, while more expensive than senior debt, provide equity content that helps support the rating amidst higher leverage.

**3. Recommendation:**
Given the substantial increase in net debt, the transformational nature of the recent M&A activity, and the need to preserve credit metrics during the integration phase, a moderate to high level of hybrid support is appropriate. While the company's size is large, the rapid increase in borrowings warrants a proactive capital structure optimization. An issuance level at 7.5% balances the need to manage leverage metrics against the increased cost of capital. An 11.25% or 15% level would be reserved for companies facing more acute "significant leverage pressure" or "material downgrade risk," whereas Bouygues maintains a strong revenue base and a clear rationale for its strategic moves.

Therefore, 7.5% of total adjusted capital is the most prudent recommendation to manage the current leverage expansion.

<answer>7.5%</answer>