The only solution to this, as far as i know, is to adjust your client rate and to reconfigure steam to a higher download speed. Maybe update your router firmware, maybe disable UPNP.
I am pretty sure donator slot has nothing to do with it. If you get kicked from the server for that you will get a message, something along the lines of
"You have been kicked from the server to make room for a donator"
I think it means the server is sending you more information than your computer can handle at once and it simply crashes. Mic-spamming is known to make this happen, but it is not the main cause.