We ordered our TT with the 15k because we live in the heat and did not want to chance the 13.5 not being able to keep up (even though most of our RV'ing is up north in Oregon and Washington). We've been in hot weather and really hot weather well over 100f, and the 15k keeps ours comfortable. If it were me and we had the same trailer with canvas bunk ends, I would definitely get the bigger A/C unit. I know it's hard to order and wait weeks and weeks, but I bet you'll be glad in the long run. Stay cool!