Are you taking your practice tests under the same conditions every time? I would do it on a Saturday or Sunday morning when you are feeling good and fresh.
1-2 PT per week is sufficient, if you do more you could burn out or see score decreases.
W…
I think you should give yourself more time to study. 15 prep tests is not a lot. Maybe delay and take the June administration?
Also, you could try out other resources, like the LSAT Demon or the LSAT Loophole book.