My last trailer had 14" wheels, the current one has 15". With these two wheel sizes, the choices of tires with high load ratings and quality construction are very limited. The first thing to have to check to make sure the load rating of the wheel on you trailer can take the extra pressure of the higher pressure tires. After lots of research over the years, I think the best choices are:
14": Kumho 857 Trailer Tire which is a trailer tire that exceeds the "ST" standard.
The only other choice I could find in load range D was be the Kenda Karrier
Kendra Karrier. They used to make a load range D (65 psi) in size 215, but now they only off it in the 205 width, but it still has a couple of hundred pounds more capacity than the Load Range C 215's.