Low performance

The performance of the game is very low. I am using a local game, not on a remote server. There is a substantial lag in the game reacting on user input, therefore e.g. quite often a block is placed somewhere instead of the intended moving of the player within the world.

When moving the player, the update of the world is done slowly (as if the frame rate would be low).

I have changed the simulation distance and viewing distance to 8 chunks and switched off clouds and beautiful skies, but this did not change the problems. 
Loading is also very slow and takes several seconds.

I am using an IPad Pro 11" (Model MTXQ2FD/A)