whenever i open my world it drops in fps to a max of 2 and crashes a few minutes later

What I expected to happen was...:
when i open the game i expected it to play like normal

What actually happened was...:
i opened my world and i got to take a few steps and then the fps drops and crashes a few mins later

Steps to Reproduce:
1. open my world
2. walk around
3. fps drop
4.game crashes ¯_(ツ)_/¯