Go with the 15k. My Laredo is set up for a 2nd air conditioner and is 50 amp even though that A/C is not installed. It will run on a 30 amp plug in and if nothing else is running a 20 will do it too. As for Open Range, friends of ours have a 5th wheel and I think its better than usual quality. He tells me the Open Range factory customer service is very responsive and helpful.
Pick up one of the Hughes voltage meters you plug into an outlet to be sure you have enough voltage to run it. Never run it below 105 volts.