My 6S Plus was only 16GB and I had storage to spare, If you keep on top of things, Delete rubbish and unused apps, Store photos off line ect ect theres no reason why 32GB shouldn't be plenty.
I like to think I keep my information fairly organized and even with a 64 GB I'm at about 75% capacity. And that's also because I subscribed to Apple Music, so I was able to free up all the physical MP3 files I had, and now stream it all. If it wasn't for that I'd be over.
I mean my keychain thumb drive has over 16 gb of storage space and it's the size of a cigarette butt.