It can also be CubeCraft....it's the internet connection:
Two possible problems:
-your internet connection is bad
-his internet connection is bad (I think that is the problem)
and cubecraft can't fix this now, I think.
and the next time post a bug/lag on: https://www.cubecraft.net/forums/bug-reports-support.35/
I'm not sure cause there was much lag b4 the merge too...I think after the mering with The Chunk they get the lag(No hate to The Chunk)