If you call that lag you should come to australia.
PvP always lags more than PvE. The more players who are interacting in PvP, the worse. Its because of the basic scripting and algorithms are interfering because of the fact that two or more characters are interacting on each other. (Im no good at explaining it in simple words, it ends up gibberish but i tried, hopefully you get the gist.)
Look at GW2 for instance they have 40v40-80v80 PvP battles, your MS will go from 0-200 to 800+. Happens to everyone, and often depends on many factors you cant do anything about.