The archive has a lot of duplicate files contained in nested Zip files.
For example, after unpacking all the nested Zips, md5sum gave results like this one:
2b5b0156c154d9755b00a1fee34a8b5e Caverns & Mines/Mysterious Cavern/Mysterious_Cavern_Complete.ogg
2b5b0156c154d9755b00a1fee34a8b5e Caverns & Mines/Mysterious Cavern/Mysterious Cavern/Mysterious_Cavern_Complete.ogg
2b5b0156c154d9755b00a1fee34a8b5e Mysterious Cavern/Mysterious_Cavern_Complete.ogg
2b5b0156c154d9755b00a1fee34a8b5e Mysterious Cavern/Mysterious Cavern/Mysterious_Cavern_Complete.ogg
When I tried removing the duplicates and repacking the files with default settings, the size dropped from 226.6MiB to 64.5MiB.
That aside, they’re beautiful pieces and I’ll probably wind up using them for the non-competitive mode in a game I’m picking away at. (Sort of a Lode Runner-esque game with more acrobatic movement and fixed-pattern monsters to make the levels more puzzle-y, where I want to experiment with procedural generation and a multiplayer race mode.)