AFAIK Tronlink only support a token that run in Tron network, even USDT is centralized and could be frozen, but this USDT is run with Tron network, so Tron team is responsible for this case. Have you ask the customer service? they should handle your case since $15K isn't a small amount money.
From your screenshot I don't see anything that can be see as locked, I think you need to find the unstake button or if you didn't find it, you can explain more briefly.
Just OP checked his USDT status, It appears that the OP has locked his USDT for staking purposes, so USDT usage is not allowed. It is not the wallet's fault, but the OP's problem. But after all, it is quite risky for him to hold the majority of his assets in USDT, as they can be frozen at any time and are somewhat difficult to recover once they are frozen.
OP! you should online and let us know whether your problem has been resolved or not.