[MC-95047] Creating/Entering single player worlds on Mac takes very long, and Mobs are always frozen and slow

What I expected to happen was...:
I would enter my single player world

What actually happened was...:
It took forever to load and then crashed

Steps to Reproduce:
1. Create any single player world and join it
2. Wait forever, then crash or be in a laggy world you can't do much in.

Related issues

migrated 2016-01-01T06:03:29Z

Happens on PC too

migrated 2016-01-01T06:05:35Z

Please attach the crash report.

migrated 2016-01-03T02:49:15Z

Crash is hard to duplicate, but the slow / frozen mob issue is far more common. Fps lag is minimal to nonexistent. I'll keep trying for a crash.