There's also:
https://mcforge.readthedocs.io/en/1.15.x/
And that site is simply an extraction of the in-code Javadoc, so its likely out of date. Not to mention that 1.16 is not fully deobfuscated yet.
Anyway, what things do you still need? I know there were a few more changes from 1.14 to 1.15 (and again to 1.16) but I've lost track of the gist for them.