Between this and my battery replacement I opted into, my 6S Plus feels brand new. If your battery health is < 85% I really suggest you take advantage of the cheap battery replacement by year end.
Amazon sells a bunch of self-install battery kits for ~$21, which has a same-or-higher capacity battery, including the tooling.
It was very easy to do the self-install, and my 6S is just really snappy. This was only on iOS 11 too. Excited for iOS 12.
The camera is really the only feature that I would upgrade for at this moment. But I don’t use the camera much.
[edit]
To answer your question, I guess it couldn't hurt? The thing is that I definitely did not trust the 81% that the battery health check was telling me. My battery would drain in minutes from 30% and the phone was practically useless in the cold.