While having someone look at my pack to see what is causing an unrelated issue, they discovered that Stellar Sky, at least on 1.7.10, is eating a lot of CPU power.

Team-RTG/Realistic-Terrain-Generation#870

If it is possible, see if you can reduce CPU usage on later versions of MC, since 1.7.10 is no longer supported by you.

Must be tested on 1.10, since cpu performance got greatly improved on recent versions.

Closing this since it's based on 1.7.10 which is a far outdated.