King__Kruppe

Tough decision to make - especially if you haven't done it before.

IMO, enjoy the next week or two or three if his condition doesn't deteriorate, but put him down before you move. You want him to still be able to feel comfort at your presence when its time, and one of the worst outcomes for everyone is something like a massive seizure in the middle of the night being a lasting memory.

He will perceive the stress of moving from your family, in addition to losing his familiar surroundings likely making the issues you mentioned worse. Plus you won't have a ton of time to focus on him while this big life change is happening - increasing your stress and making you feel like shite.

15 years is an awesome life, and while you are holding on for him - he is doing the same thing for you and your family.