Interesting question. We just made the leap from our HTT with a 13.5 to a TT with a 15. We never had a problem with the 13.5 until a trip to Vicksburg, MS with 99/99%. Could not get the HTT cooler than 85 during the day even with the PUGS on. Made a Walmart run and got some small personal-size fans thinking that would help in the bunkends, but wrong. All it did was help move the hot air around. After sundown, it cooled off nicely.....until the next day. UGH! The dealer we bought the TT from orders 13.5 A/C routinely, but for whatever reason, this one has the 15. In what I'd consider "normal" summer weather, does anyone notice any difference in performance/efficiency/operating costs in the 13.5 vs the 15. We're not headed to AZ for sure, but TN has some pretty darned hot/humid weather. We keep our TT under cover 24/7 at home, but also keep the A/C set at about 80 since we're in and out all the time. Am I going to drop over when I see the electric bill with the 15 now?? I never noticed any appreciable difference when we started keeping the HTT plugged in over not.
FWIW, if this AZ visit is not going to be a routine thing and the 13.5 is normally effective, I'd look into that portable unit that was linked....at least for the short haul. It may do all you need for a bunch less $$$.