Big entity and redstone lag after switching from 1.12.2 to 1.15.1

After switching from minecraft version 1.12.2 directly to 1.15.2 , redstone is very slow.

Also all entities are lagging (minecarts,items when thrown on ground,)

Eating food takes a long time and when mining dirt or a block with longer mining time , the block stays for a few second, then decay.

 You can see a video of this behaviour here and my world here :

 

https://www.dropbox.com/s/wm8nga1gph6yd65/Video%20%2B%20My%20world.zip?dl=0

 

Have a nice day.