The question has been posed many times, how much AC do you need. It is hard to find the requirements for RV AC units. The FIRST thing you look at in a household window unit it square footage of the room. A 25' long interior RV space with no slides is about 200 sq foot. Adding 3 slides like ours might add another 75 sq feet. Looking at a chart for hh units like this one https://learn.compactappliance.com/b...ng-calculator/
it calls for 7000 BTU's to cool 300 Sq ft. And this assumes 8 foot ceilings so RV's usually have less cubic footage to cool. But of course the insulation is not equal to a stick built home either. I looked briefly for any estimation of square footage ratings on RV AC and didn't come up with it. Maybe someone on the forum has found it?
But it seems like one 15000 BTU unit is double the requirement of the size required for a 300 sq ft space in a house and should do a decent job in normal outdoor temps for a well built RV OF course if you are going to Phoenix or Vegas in the summer, all bets are off, but personally I wouldn't be caught dead there at that time of year.