[1.15.2] java heap space error

https://www.dropbox.com/s/16sdr3aqsxlphh0/debug-1.log.gz?dl=0

Yes you have a mod that causes memory corruption in your savefile...

at net.minecraft.nbt.CompoundNBT.func_229680_b_(CompoundNBT.java:431) ~[?:?] at net.minecraft.nbt.CompoundNBT.func_229680_b_(CompoundNBT.java:431) ~[?:?] at net.minecraft.nbt.CompoundNBT.access$200(CompoundNBT.java:27) ~[?:?] at net.minecraft.nbt.CompoundNBT$1.func_225649_b_(CompoundNBT.java:43) ~[?:?] at net.minecraft.nbt.CompoundNBT$1.func_225649_b_(CompoundNBT.java:30) ~[?:?] at net.minecraft.nbt.ListNBT$1.func_225649_b_(SourceFile:48) ~[?:?] at net.minecraft.nbt.ListNBT$1.func_225649_b_(SourceFile:31) ~[?:?] at net.minecraft.nbt.CompoundNBT.func_229680_b_(CompoundNBT.java:425) ~[?:?] at net.minecraft.nbt.CompoundNBT.access$200(CompoundNBT.java:27) ~[?:?] at net.minecraft.nbt.CompoundNBT$1.func_225649_b_(CompoundNBT.java:43) ~[?:?] at net.minecraft.nbt.CompoundNBT$1.func_225649_b_(CompoundNBT.java:30) ~[?:?] at net.minecraft.nbt.ListNBT$1.func_225649_b_(SourceFile:48) ~[?:?] at net.minecraft.nbt.ListNBT$1.func_225649_b_(SourceFile:31) ~[?:?] at net.minecraft.nbt.CompoundNBT.func_229680_b_(CompoundNBT.java:425) ~[?:?] at net.minecraft.nbt.CompoundNBT.access$200(CompoundNBT.java:27) ~[?:?] at net.minecraft.nbt.CompoundNBT$1.func_225649_b_(CompoundNBT.java:43) ~[?:?] at net.minecraft.nbt.CompoundNBT$1.func_225649_b_(CompoundNBT.java:30) ~[?:?] at net.minecraft.nbt.CompoundNBT.func_229680_b_(CompoundNBT.java:425) ~[?:?] at net.minecraft.nbt.CompoundNBT.access$200(CompoundNBT.java:27) ~[?:?] at net.minecraft.nbt.CompoundNBT$1.func_225649_b_(CompoundNBT.java:43) ~[?:?] at net.minecraft.nbt.CompoundNBT$1.func_225649_b_(CompoundNBT.java:30) ~[?:?] at net.minecraft.nbt.CompressedStreamTools.func_152455_a(CompressedStreamTools.java:121) ~[?:?] at net.minecraft.nbt.CompressedStreamTools.func_152456_a(CompressedStreamTools.java:91) ~[?:?] at net.minecraft.nbt.CompressedStreamTools.func_74794_a(CompressedStreamTools.java:87) ~[?:?] at net.minecraft.world.chunk.storage.RegionFileCache.func_219099_e(RegionFileCache.java:49) ~[?:?] at net.minecraft.world.chunk.storage.IOWorker.func_227102_b_(SourceFile:83) ~[?:?] at net.minecraft.world.chunk.storage.IOWorker.func_227112_h_(SourceFile:186) ~[?:?] at net.minecraft.world.chunk.storage.IOWorker.func_227107_d_(SourceFile:131) ~[?:?]

I am not sure what it is but i can assure you chunkpregen does not even touch saving itself or how saving is done in mc...

This is a memory corruption. And this causes the issue.