I also have an 6s. Haven't found much reason to upgrade. I like the smaller form factor. I guess upgrading to the 7 or 8 may be nice at some point for water resistance (a heavy rain shower killed my SE).
I switched from 6S to XR, and I wasn't expecting much, but oh boy, you don't realize how much of a difference a boost in processing speed and screen size can make. Massive productivity gains, even though I'm primarily a desktop person. That plus the huge battery on the XR fundamentally changes how you think about your phone.
I don't really use my phone much anymore besides for calling, messaging and occasionally checking email. Whatever productivity boost I'll get on my phone doesn't matter much in practice.
Battery life is also no problem. The 6s makes it through the day and I charge it overnight.
