13.5 AC versus 15.0 K AC

Dealer has two travel trailers that are exactly the same except for the air conditioner units. Any disadvantage to the 15.0 k models? Early freezup etc.? Either will be adequate for the trailer as it will be parked under a carport. I have a similar model with the 13.5 unit and it does very well. The 15.0 k model is the same price, so the only question is about efficiency and potential problems.