What would stop me from using a 6s is the fact that it’s no longer getting security updates. Sure, you’re unlikely to be hit with the nasty stuff unless you’re a person of importance/annoyance to power. But once the cat is out of the bag, typical hackers can start looking into how to do the same. You don’t have to throw your 6s away but I think your overall experience would be better. Even a new battery won’t fix the fact that Apple isn’t going to be sending out (very many) bug and security fixes to your device. At the very least, you could use your 6s at home as a music player or photo album or whatever.