If the games have been working fine but suddenly are running slowly, it may be that your web browser is running low on memory.
One thing to try is to close all of your browser tabs and then reboot your computer. When you play a game, only have one browser tab open and see if that makes a difference with the performance.
Another thing to try is to use a different internet browser. If you are using Safari for example, try using Chrome or Edge to see if the games work better in another browser.