The issue may not be with the server, but with how players connect to the server.
Internet connections volley from point to point to get from the client to the server. If even one of those points are experiencing a slowdown or a technical difficulty, it could drastically slow down traffic between the server and the players. Especially if the source is closer to the server, as it is more likely to be used as a relay point for more players.
These issues are usually fixed within a week at most. So give it time.