Low TPS when moving over y=200 in ocean biomes

Steps to reproduce:

• create new world
• move to ocean biome (e.g. /locate Monument)
• move above ~ y=188

Expected:

• tick time will stay constant

Actual:

• tick time moves from ~20ms /tick  to >200 ms/tick

 

Further Information:

• Can't keep up messages in server log
• profiling via /debug shows "Test World.tick.entities.regular" as a main culprit (log attached:profile-results-2018-08-25_15.02.46.txt)