I have many sites in my MainWP dashboard which leads to heavy loading times. This seems to be because all child sites loads at first and then there seems to be some ajax going on and finally renders the pagination.
Seems a bit odd to load all child sites and then add them to pagination leading to heavy load.
This is our biggest issue with MainWP right now slowing down our work progress 
Suggestion:
Only load the number of child sites set in setting posts per page in MainWP.