My most extreme personal experience has been when my trailer is at my house in Southern AZ (loving the new 30-amp outlet so I can actually run the AC here)...I agree with cranking it very cold in early AM and it will maintain better throughout the day versus waiting until it gets hot then turning on AC. Even moreso I agree with Desert Captain in escaping the heat and going where it isn't as hot...not always doable though.
I don't think you'll see a major difference between 13.5 and 15k though. Any way to add a second unit (maybe lower profile) to your unit? My neighbor added a low-profile unit in the front bedroom of his 5th wheel and made a big difference.
Interestingly on our summer trip one of the hottest days was when we were in Glacier...no AC in the trailer since we were in our friends' driveway plugged into their 15/20-amp outlet. Took the trailer a while at sundown to cool off.
