Is a 13,000 BTU AC enough for a 22' trailer?

To OP, For your size TT, 13.5K will work fine.

Our Jayco 23RB is 23.3' long box, (280"), or 187 sq ft, and the 13.5k A/C cools it just fine. I don't know if being ducted forward to the bed area, to the bathroom in the rear, or the living/galley area in the middle helps with the overall cooling or not.

If I were ordering one brand new, I'd go ahead and opt for the 15k unit, since that option at Jayco was only about $150 more and a little more never hurts.

We've got a 29' box with only a 13.5, and it does ok. At the beach with no shade and mid day temps around 97-98, it could not keep up, and the inside temps got to the mid 79's.

I found lots of heat coming through the bathroom. I cut foam to fit in the skylight, and vent opening, and that made a huge difference.

The smaller unit might be easier for a portable generator to handle if there will be any future dry camping... we had a 24’ trailer with a 13.5 in it and you could hang meat inside.

I have a 23' Jayco 23RB. The 13.5k BTU A/C keeps the trailer plenty cool. You should be fine with that size.

Now, if I were special ordering a new TT, even of my current size, I'd go ahead and op for a 15k unit.

Said another way, a 13.5k unit would never be a deal killer, but if I had a choice, I'd opt for the 15k unit.

We had a 25’ TT with a slide and 13.5K AC. Even in 100 degree days, no problems.

As was said the 13.5 will be OK, but given the option I would go bigger. It will cool off faster and maintain temp better.

It should work out fine assuming it's a quality AC that is functioning properly.

The 13 may work but you will be happier with the 15.

I had a 23.5 x 7.5ft trailer with 13.5 non-ducted and it was okay but noisy. I don't know how the models you have to choose from would compare in noise. However the most important factor may be whether you have a generator that could run one but not the other.

I also think the 13.5K BTU unit will work, but if I had the option of 15K, I'd be all over it.