I am going to make a couple of assumptions here. First, the server is run locally, if not from the machine you are playing on. The second would be that you are all experiencing lag, not just yourself. Provided your machine has enough RAM to allocate, I would change the min and max RAM for you server. I currently have "java -ms1G -mx2G" and I seem to be able to have about 6 or so people on with no lag what so ever. Also, if the server is run locally, check you internet connection. Could be a bad day from you ISP. If nothing else, I think this would be a starting point at the very least