Internet explorer is a dinosaur when it comes to flash based games, and it probably on the bottom of everyone's list of browsers to use for flash gaming.. It works but it is slow..
Google chrome is much better but has a lot of other functions that come with it that slow it down.. Most of these functions that slow it down are from their web tracking, the what you do and where you go and what you do while you are there, so that they can compile user profiles, which they in turn sell to marketing companies so they can better know where to put their adds... And yes you agreed to all of that by simply using chrome..
Clearing your browser cache frequently will help with speeding it up again for a short time.. every time you see it starting to act funny again just clear your cache... this should fix a lot of problems you are having while using google chrome... Also sometimes when they update chrome it throws the flash player out of whack..
I'm not sure what the recommended browser for this game is, but I use edge and so far have only really had a few problems using it on this game.
Now using edge on an older windows platform may cause it to work a little worse, since edge was designed to replace internet explorer on windows 10.. Funny thing is when you try and switch your browser on windows 10 it lets you know that edge was specifically made for windows 10 and not to use another browser..
I have heard nothing but good things about firefox, but I have yet to try it..
I'm by far not a tech when it comes to these things, but I do play a lot of browser games and read through each games forums and these seem to be the most of the answers on them 1) try a different browser or 2) clear your browser cache..
Hope this helps
Edit: I almost forgot, that before you clear your cache go remember all your login info and passwords for everything you use, because clearing your cache will also clear the saved information from the browsers autofill / autoremember