Earlier quoted context omitted.
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.
Battery life is also no problem. The 6s makes it through the day and I charge it overnight.