We're sorry to hear about this. Could you please let us know when exactly the app gets slow? Is it happening while using the overall app or using any feature? Which browser are you using?
Have you tried using the other suggested browsers (Safari, Microsoft Edge, and Google Chrome) to see if it makes a difference? Such problems can also be fixed by clearing the browser's cache and cookies. Please check this link to know more on how to clear cache and cookies: https://support.google.com/accounts/answer/32050