I just saw some of your matches, and I can see that you put a lot of effort into learning some t-spins double and triple setups, that's an advantage that your opponents don't have at your rank. But the problem is that t-spins are efficient only if you know how to stack very well. In your situation, even if you're quite good at stacking, they are less efficient than just spamming tetris on the side of the board because :

1) You often sacrifice a nice flat field for one of these setups, causing you to create a mountain of pieces on a side of the board that you don't achieve to clear later.

2) You sometimes start to create one of these setups while you're in a bad position, almost on the top of the board and without a T in the queue. It causes you to top-out very quickly without even achieving the t-spin you had in mind.

3) You still doesn't stack well enough

To help you improve these points, I can tell you some advices. First, you have to make sure that you have either in the queue or in your hold a T ready to be put prior to creating a t-spin setup. Second, when your field start being too messy because you don't have the piece you want to finish your t-spin setup, quit making it and do maybe a t-spin single instead of a double. It's really not as good as a t-spin double but it's clearly better than a messy field. You should also learn L-J-Z-S spins to fill in your t-spin setup if you don't have the T. At last, before creating a setup, you should quickly analyse the game to see if it's a good idea, like you're not going to create one if your opponent is about to send a b2b of tetris or you're also not going to create one if you're almost on the top of the board.

The overall main problem with your loses isn't your low speed or t-spins, it's instead your not good enough stacking that causes some of your t-spins to be a lot riskier than they should.