Everytime I covert my world I lag the entire game, plus I don't get my entire world.

While in the middle of converting the world I will sometimes pop open the snap menu because the waiting is so long, when I do the frame rate will drop on it a lot so I cancel It to let it complete the conversation. Sometimes the conversation don't go through at all, my entire game will crash and power down to restart/reset. Same thing when I complete the conversation the game will restart on its own (sometimes). What I am trying to say is that Minecraft will start to act up everytime I convert my world. The size of the world is 111.9 MB but when I covert it it's 21.4MB but the numbers are always random, the highest I've gotten was 40.6MB. I will send pictures with the description, I hope I've said everything clear enough. This a add on message, I forget the most important thing. I will have to restart my game everytime I convert my world because when it finally complete my snap menu don't want to pop out, my game will freeze for a minute until it brings me back to the game. So I restart it because of that...