Still crashing when going through Nether Portal.

Have the issue since the last month that everytime i go trough Nether portals on my World the whole game crashes. On other worlds it it works fine but on my very first world it keeps crashing. What could i possibly do erong or how can i fix this? I don‘t wanna lose this World because me & my best Friend are building on it Since 2012 and it would be a nightmare to lose that world

Would love to see an solution for this 

 

Greetings Foefi