After rechecking everything, I've noticed that my board was missing one jumper. Without that jumper the cache is very unstable. Right now I can push the original cache to 0/1 WS (Read/Write).
EDIT: No, it's still not stable, but at least that's a progress.
EDIT2:
Another batch of perfectly working 15ns SRAM and another failure. I give up. It's just a sh*tty board through and through. It's incredibly picky with SIMMs, SRAM and the CPU doesn't work stable at 100Mhz. Doesn't worth all that hassle to make it work properly. Good thing it didn't cost me much.
EDIT3:
And even more surpisingly, all my problems with cache disappeared after I've installed 486DX. Heck, I can even overclock it to 40Mghz with 0 WS. What is wrong with that board?!
I must be some kind of standard: the anonymous gangbanger of the 21st century.