Wow Fuzzy, I love hearing about all your quirks; what a character you are. And age 15? Good work; you look healthier than my 18 yr old boy at home; I wish he was doing as well as you. Hope you are here for years to come, and don't worry about the thyroid issues, I have them too!
As I told Fuzzy, try some "Kidney Gold" fka "Tripsy" with your older cat. It has great reviews, and you can get it on PetWellBeing.com. Older cats are prone to kidney failure, it's very common.