I have had my TT for 11 years now, and the previous one for several years before.
I have experience with the marginal quality Chinese ST tires.
I am very particular with the tires.
Always check PSI before a trip. Always covered when not traveling.
Trailer weight checked. Not overloaded, but at 90% of factory rating.
ST tires seem to last 1-2 years before cracking, or in the case of the last set, they looked fine, and I lost 3 on a 500 mile trip.
Emailed Michelin, Goodyear, and others. All had LT tires they recommended for trailer use.
I said no more. Bought 16" wheels and LT tires.
My tire guy highly recommended this plan. Went with BFGoodrich Commercial T/As.
My tire guy said that all ST tires in 15" he could source were made in China with the exception of Maxxis which were Thailand.
He also said ST tires all have a 1 year warranty. The BFGoodrich have a 6 year warranty, and that even covers sidewall cracks in storage...
Also, upon further research, ST tires are subject to the same testing as gold cart tires and wheelbarrow tires....Not very confidence inspiring. They get around this, by the "not for passenger vehicle" wording on the sidewalls. LT tires are subject to much higher standards.
I also found that the NHTSA doesn't really follow-up on complaints as these are not passenger tires, and should not be causing injuries....
My conclusion.....
ST tires are a way for tire companies to make a price point dictated by trailer manufacturers. All the BS about them being better for trailer applications is total ****. If the manufacturers stood behind the tires, you would get better than a 1 year warranty.
Personally, I will trust a tire that IS rated for passenger use.
My .02