Sure our usage are very very different, I don't need low power mode, my 6+ never run out of battery. So, it won't affect me.
I only installed few tweaks, mainly need F.lux, the native one works well for me. I don't need the extra settings, but just the basic function. I don't need phone call in Super HD, in fact, I don't know what it is.
However, 9.0.2's animation is not that smooth for 6+ (I have another 5s still on 9.0.2jb, which is totally fine). It won't affect the iPhone's basic function, but if I don't really need JB anymore, why not get it as a bonus.
Haha, of course I don't need Facebook in 9.1, but some new apps (e.g. for quick photo editing etc) really need 9.1 or newer. In fact, some Bank apps will show me a warning (about not secure to run on a jailbroken iphone) and refuse to run on my 6+, which make me hard and hard to stay on 9.0.2 JB.
Of course, what I mean improve performance is mainly on the UI, not the background stuff. However, that's the interface, which do affect me. With few tweaks installed (may be I simply pick the wrong one), my 6+ sometimes need few seconds to switch apps (back screen for 3-5 sends), I really hate that, especially when I am at work, I really want the phone respond to me ASAP.
Anyway, I will keep my 5s and ipad 2 jailbroken, but I am also happy to give up JB on my 6+. In most of the time, I prefer to use the phone in the native way. I jailbroke it because I want to make it easier for me to use, but not make it special. And it cannot serve this purpose at this moment on my 6+. Hopefully the official 9.3 will be jb avail, I will then JB it again ASAP. But now, I am happy to use the 9.3 beta rather than 9.0.2 JB on my 6+.