I doubt chess.com is slow your computer is probably slow you might want to get a new one if you can afford it.
Otherwise, you might try a different browser
Also try this https://support.google.com/websearch/answer/6283840?p=speedtest&visit_id=637104839038019875-4043449989&rd=1
To test your internet speed under 40 is good but 35 is pretty average unless you have a nice computer.
I have 300mbps internet which should handle a simple chess game. I can play any number of much more intensive games such as starcraft 2 and overwatch with no internet issues or computer issues. Chess.com is just really having a hard time providing the bandwidth on their servers for the users it has.
I mentioned it before and I thought most would have understood it but here it goes again. For those of you that are old enough to remember what it was to play chess on Java you would remember how it was connection driven. Those with a good connection will not suffer latency issues while those with a poor connection will unfairly pay the price.
Roll fairness an equality and time stamping offers the possibility to play chess at a more reasonable level. You move the move gets registered your opponent moves and it gets registered with their own time stamping. This feature is available here at chess.com to turn on and off. This means that if someone has around 300k and you have 25mbps your moves will not be any faster because you need to wait for your opponents move to register. So it will appear as a slow bullet game.
Now apply that to someone that pays for a 1gig line and you come up with a mere 100 mbps then it will appear to your opponent that your moves are not fast enough. On top of this you need to account for server location and how long does it take for your machine to ping the server. All these handshakes are made -- plus the coding of the site and you end up with a faulty service.
For a flawless-ish service chess.com would have to have servers close to every single one of the users and also not allow those who don't have a connection and that seems pretty fascist. Chess.com does not have that availability and even if we all paid top price they will still be unable to do that. It is chess.com not Google.