Abnormal mob spawn rates

Put the summary of the bug you're having here

What I expected to happen was...:
Have normal mob spawn rates

What actually happened was...:
There are too many mobs spawning

Steps to Reproduce:
I don't know what's exactly the cause. One possible reason may be that I have the render distance at 2 chunks to avoid massive lag and chunks have trouble loading, and this may cause the mobs to only be able to spawn in close distance around me.