Hello Aternos Team,
could the mod "ChunkGenLimiter" be added to your mod list?
Link: https://www.curseforge.com/minecraft/mc-mods/chunkgenlimited
ChunkGenLimiter significantly improves server performance in terms of Chunk Generation by fixing Minecraft's default set absurd chunk loading values, those values being chunksPerTick and maxChunkGenMillis. Due to the possibility of the chunk generation being overloaded, this can slow down other aspects of the game.
Really hope to see this mod on 
Have a good day,
vonotige.