Here is a recommendation for you. Photo storage will never become an issue if you do these 2 things:
1. Get Google Photos. It provides simple backup just by opening the app. Once they are in the cloud, you can consistently run workflow (#2 below) to clear your camera roll.
2. Get Workflow App on the Appstore and get the "Clear Camera Roll." You can place it on your home screen and run it with one click.
This is assuming you are comfortable with Google Photos...some people do not like being a product; however, I think it is a bad ass service. The speed, ease of searching, facial recognition, etc. Its great.
Yeah I have Google Photos, but for some reason I still can't hold more than 50 or so pics on my phone without it saying I'm out of storage. I don't even have a lot of apps. Maybe texts or saved snaps? My 6 is on its last leg anyway, shattered screen, scuffed up, slowed down. Need a new 7, hopefully 32 will be the standard.