World runs on extremely low framerate, and then potentially crashes

My game always runs on a smooth 60fps. However, this time when I entered my world, it was running around 20fps and the chunks were taking quite a while to load. I then exited my world and loaded it again to see if that corrects but it didn't do anything. For some reason, all entities and signs loaded first. Later, I entered my settings to lower the render distance to see if that would help, but then my game just crashed.

Other times, my world will just crash on startup.

 

THINGS TO TAKE INTO CONSIDERATION:

• I was using default textures
• My multiplayer settings are disabled
• Redstone is not used in my world