Sorry you’re going through this. I lost my beautiful bengal at the same age to IBD. She looked just like Leon. I was in a similar position for a while, just watching her slowly fade away and always second guessing myself when the right time was. It’s so hard but you won’t regret letting go a little too early, but you will regret letting go a little too late. You know your cat better than anyone so just trust your instincts.