Hello,
i play with friend trough LAN, and after 30 min, or even less we experience big lags, but only when we facing bigger groups of mobs, or just combat. Without combat, everything is smooth. So i guess its not connection speed problem.
The one who host game is alright, its problem only for joining player.
Can anyone experience same problem? Can someone help please? Its unplayable… 
Thank you
Cmx