Minecraft world bug!

So my world that I created in Minecraft 1.13 got converted to Minecraft 1.14 but any time i go to the nether it lags really hard.

Every few seconds my cpu gets overclocked and the game freezes for a bit. It’s unplayable. I tried choosing the lowest graphics minimizing the screen vsync on setting the game’s priority to high and restarting the game in the nether.

I also stayed afk in the nether for half an hour so maybe everything would load…

Nothing. Nothing helps. Any suggestions?

Did anyone tried new Minecraft 1.14.1? Is it any better? If not is it possible to convert my world back to Minecraft 1.13 and use that?