ZLTweaks

This is a 1-1 carry-over from 1.14 to 1.15 and up texture-wise.  The only change is that the pack.mcmeta has been updated from "pack_format": 4 to "pack_format": 5.

Features:

Glass top shades now match more closely to glass sides.  This includes colored glass.  They used to be a single color, just with varying transparency.  They now have same shades as their respective tops.

Mod support:

Biomes O' Plenty:  Fixed tiling on doors much like with the vanilla doors, unique textures on sides/top/bottom.  Didn't take as long as I expected.  Lots of files, though.

Bunch of Biomes:  Clay Dirt had its texture renamed to clay_dirt instead of claydirt to more closely reflect vanilla's style.

Bunch of Biomes:  Simplified block shades of mud and clay dirt to 8 shades each.

Fabric Mod Support:

Modern Glass Doors:  Fixed tiling and slightly changed textures on the doors to my liking.  Especially noticeable on tops of oak and iron.  Required less files than normal since they're already based on vanilla textures.

Optifine + Mod Support:

Bunch of Biomes:  Vanilla grass and Cursed Earth overlays mud and clay dirt.

Optifine can be downloaded externally here.  Made using latest version (including preview version).  Preview versions can be viewed by clicking the link called "Preview versions" at the top of the downloads page.