When we had a Class C with a 13500 Coleman Mach A/C, we could run it on a 20A branch circuit that had nothing else on it. I don't think that setup would run the 15000 unit on our present RV.
Part of the issue will be your adapter and any extension cord(s). I installed a 30A RV Receptacle and weatherproof cover so I could use the RV's shore tie cable and no adapter.
How old is your RV's A/C? If more than a couple years, have you cleaned it? I thought I'd have replace the old 13500. Cleaning the Evaporator at the front of the unit (requires removing shrouding) restored good performance and that A/C was over 20 years old.
