Closing a bedroom door does little unless you can also close or block off the vents in there. You don't say what make and model your travel trailer is, but not all are created - or insulated - equal. IMHO, 15K is not a lot of AC for a 33 ft. TT in the conditions you are describing. We have two Coleman Mach 15Ks on our 35' fifth wheel and they keep the inside of the coach at 72 - 74 with temps in the low 90s and heat indexes in the upper 90s (plenty of humidity in the mid-Atlantic states right now). Is your RV prepped for a second AC?
Rob