I had the same problem when I had a server on a DSL connection.
Sounds like this server has to much to do or SSM code is humped.
Or clients have to adjust there graphic settings.
Server spec?
Extra vehicles makes lag for clients sometime.
Try no patchfile or a patchfile without vehicles and gather 20 people and test lag.
PS.Nothing wrong with moonshine!
Guess people in countries with bad connections can be angry at it, US for exampel. I only had complaints for them.
-"This is to laggy, can't move!"
You tell them to lower graphic quallity to lowest to avoid lag.
Response will be....
-"I got a Duo Quattro stagioni with multiple sideburns and 40gb of cache."
You tell him it doesn't matter, reduse graphic quallity and you will be fine. Server don't lag, only uses 8% cpu at moment.
-"You run server from home, no wonder it's so laggy!"
Some pissed of Canadian, Aussie or Jap with a P3 and only 256mb ram tell him to shut up after a while, couse they followed our advise about graphic settings and got a baby smooth game after that, at a ping of around 300. In BFV.