Complicated FPS Issue Related To My World - FULL Video & Commentary Explaination

I've posted this on here before but not been resolved. Everything is explained and demostrated properly in the unlisted video I made...

 

World Download: https://www.mediafire.com/file/zrfjg5nqmxd9kf7/The_Minecraft_Venture_-_Metricate_Mojang_Upload.rar/file

Full Video Demo with Commentary: https://youtu.be/FZyD4852biY