We opted for the optional upgrade to the 15K AC unit.
In our old TT (a smaller trailer than we have now), we experienced a few days where the temp was in the mid 90's. The 13K AC unit seemed to struggle to keep the temp down to a comfortable range inside our unit.
With that in mind along with my general belief with many things in life, that 'too much' is infinitely preferable to 'too little', we ordered the 15K AC in our new trailer.
FWIW: That line of thinking also directed my decision of turbo diesel over gas when I bought my truck going on three years ago.
FAA licensed A&P aircraft mechanic, ex-RV dealer parts dept
Retired B-52 Gunner/Flight Examiner, B-52 Crew Chief
2016 Jayco Eagle HT 29.5 FBDS w/ 15,000 BTU AC, 50 amp service, upgraded counter top, thermal pane windows, elec. stab jacks, outside grill, backup camera and MORryde pin box.
2011 GMC 2500HD DURAMAX/ ALLISON