So for a server, I've generated a world (pregenerated r=8000) blocks with the 1.12 biome bundle mod (adds no new blocks, just makes world gen better), and I want to get that generated world into the latest version of Minecraft. At first, I just tried to load a copy of the world in 1.15 however this froze my client and never appeared to do anything. Out of curiosity, I loaded another copy in vanilla 1.12, which loaded and appeared to have all the chunks as they were in the modded version. I then attempted to load this in 1.15, which loaded, however, chunks which had not been generated by me in the vanilla 1.12 version were resetting back to vanilla generation. My next two attempts involved copypasting the region files of the world into a 1.15 world and another attempt involved using NBTExplorer to change the version in the game file, both of which resulted in a dozen or so chunks squared around the player working as intended, and all other chunks using vanilla generation. Does anybody have any clue how I can get this to work?