The 15" tires seems to rub, so I don't want to keep this size. Do I go back to 14" and load D(2040lbs). Or to 205\65r15 light truck tires(1874lbs)?
If the 15" tires are rubbing I wouldn't put 15" back on the trailer.
The 205/65r-15" tire sounds like a P tire not a LT. The 65 series tire is a wide base tire and not the best choice for a trailer as they require a wide wheel and a 65 series tire may rub inside the wheel well.
A LT tires capacity is not derated for a trailer but only the P tire is.
I see lots of folks with the smaller trailers going to the Kumho 857 after having issues with their brand of ST tires. Doing so eliminates any ST tire type issues from all brands.
As other mention whatever tire you choose pay attention to its wheel requirements for width and pressure. Tires and wheels are matched for best long term performance.