The 13.5 A/C will not cool rear bedroom on DP. What to do?

Need a lot more info. Year/Brand/Model of motorhome. Ducted or NON ducted. Your problem is the opposite of what most RVer's have. Due to the Bedroom having to turn over less volume of hot air, the bedroom AC usually makes it quite cold in the bedroom. Are you positive that the rear AC is cooling at all? going from 13.5 to 15 will not create a greater cooling factor. Will help a little but if NOT hardly cooling with a 13.5, then the extra 1500 will not help that much more for the cost.