Hi,
I am running More-Planets-1.12.2-2.0.15-GC181.jar on my server. Besides the minecraft worlds, forge tps reports that 2 worlds have been visited: diona and nibiru. The server produced a debug printout with the text:

[06:10:31] [Server thread/DEBUG] [FML]: The world 20b34212 (world) may have leaked: seen 1750 times.

Apparently this is due to your mod not unloading all chunks when it should.

I've already fix this issue in 1.13 branch. I'll push the fix into 2.0.16.