I love these absolutes like "All RV A/Cs shoudl be on 20 amp breakers"
FOr 13,500 and 15,000 BTU units. I'd say that is likely true.
But they make some smaller units that might well take a 15.. Don't know as I don't have one. (I have twin 15Ks)
However I'd be interested in knowing if the problem is;
1 Breaker on generator
2: Breaker on Inverter or sub panel
3: Burned connection.
NOTE that most RV wiring is not really up to 15 amps. The "Quick Box" type outlet (Brand in my beast) are **** in my professional opinion. Space heaters and other big loads toast 'em to a crackley crunch on occasion. and that's not good.. I lost one myself. as well as two wire to wire connections (Stranded to solid) I put in 12 ga fed 15/20's for space heaters NO problems period .