TPS just comes with practice, you'll naturally speed up without actually working on TPS. Anyway, you shouldn't worry too much about TPS, as it will make a difference when you are faster (your average is close to 20 seconds right?). For instance, I am sub-12 and my PLLs are almost the same speed as yours so I'd recommend working on look-ahead and F2L, and when you're faster you'll automatically have faster PLLs.