There is no multiplayer server without lag. As well, mods/admins and Sawine are still working very hard trying to get the server up to date (with pluggins, I mean). When they are working on these, there are times when the server will lag like crazy. It happens often enough for me to be used to it. I'm sorry that the game is not enjoyable with this, and I'm sure the mods/admins are also sorry for any inconvenience. However, I'd like to request that you remain patient when things like this happen. For me, if I experience lag I first log out then back in, and if there is still a lot of lag I'll restart my computer. If that doesn't work, I restart my router. If that doesn't work, then I restart my modem. If that doesn't work, then there is a problem on the server's end.
If you use a router, I'd suggest restarting it at least once every three days (not reset, just unplug it for thirty seconds then plug it back in). For the modem, I'd suggest restarting that probably once every two to three weeks. This is just so you can keep at an optimal speed on your end.