I was having trouble with 15" tire blowouts on my 28' enclosed. After quite a few blowouts with Carlisle, Titan, Tuff-tow, Heritage and any other brand I could find I finally got this info.
Denman Tire co makes a 15" 10 ply tire that I finally bought a year or so ago and so far no problems. seems to be a btter tire and I swear I can even tell the rolling resistance of the trailer is less with the extra air pressure that goes with the load range 'E' items.
These are a ST225/75R15
I found these at a local Pomp's tire store but they have a web site that might help you find a dealer near you.
http://www.denmantire.com/
Hope this helps