What size generator to run AC??

Champion 2500 dual fuel will run a 15k even on propane, what it won't do is run that and anything else but lights and tv. Your fridge would need to be on propane (with a 12V compressor fridge you'd need solar and to turn off your converter) and no microwave or other big appliances like a coffee maker. You can step up to a 3400/3500/3600 watt unit to alleviate those limits but you pay in weight, cost, and fuel consumption (both max and min burn rates).