This clearly untested game suffers from a LOT of slowdown.
So this conversion to FastROM makes the game runs at 3.58 MHz instead of 2.68 MHz.
Slowdowns will still happen due to poor programming, but not with just 2 or 3 characters on screen like before.
Now the game is much more playable.
Database match: Super Back to the Future Part II (Japan)
Database: No-Intro: Super Nintendo Entertainment System (v. 20210222-050638)
File/ROM SHA-1: DD95D3F729E9373322904F92B9816AE02B4C45F6
File/ROM CRC32: B367D0B9