It was recommended we go up to the next size. We didn't because of the cost of new wheels, but if the tire and wheel will fit inside the wheel well on your trailer, you can do it.
Although I didn't fine where Freemaster tires are made, I have checked reviews. The 15inch D tires got high reviews on Driving life.com. I have seen a few reports of a few failures on 14 inch C tires. The tires on my unit were on it from the factory to my knowledge.
OK, I found some 14 inch "D" rated 8 ply radial trailer tires. The specks show a much better side wall. Cost more but should give better service. Carlisle brand.