Integrated / "Vanilla" Snapshot Server's CPU usage is 10 times higher than in 1.13.2

Steps to reproduce

1. Run MC 18w44a Server or Client with integrated Server (happened too in 18w43c, for previous ones I don't know)

2. Create a new superflat world defaults settings, set doMobSpawning to false and /kill the existing mobs. (for comparing purposes).

3. Idle (in the case of a Server, let it run with no player on)

4. Repeat the same steps with MC 1.13.2.

Observations

MC 18w44a constantly runs at at least 100% of Core usage while under the same environment, MC 1.13.2 only needs 10%.