I went from the XR to the 15 Plus and love it. I previously had the 6 Plus. I debated between the Pro (not Pro Max) vs Plus quite a bit. After my wife got her 15 Pro and I kept looking at the screensize, the 15 Pro felt too similar in size to my XR and it's not as big of an "upgrade" for me... In the end, I wanted a larger phone and didn't care about the extra pro features. I actually ended up ordering the 15 Pro (and immediately felt buyer's remorse), just to cancel the next day and ordered the 15 Plus. No regrets at all!
I'm loving the larger screen and the battery life. Especially getting older and older, my eyes appreciate the extra screensize, especially when I enlarge text! I can play Pokémon Go for a while with the family without the battery dropping like crazy. It feels so different than my XR so it feels like a huge upgrade. The weight from the XR to 15 Plus isn't too noticeable. In the end, the 15 Plus is a perfect match for my preferences.