If needed what genny would power at 15,000 btu ac

Dual Honda 2000i's would be my first choice. You can run only one if you don't need the A/C.
A Yamaha 2400 runs the 13,500BTU AC in my brother's 5er, I don't know if it would run a 15,000BTU unit or not.
I see you're in NY. We like some of the DEC campgrounds and that's no-hookup camping most of the time. Unless we're in a site that has full sun we've never really felt the need for AC. But if we go on an extended out of state trip we book full hookup sites.