The Core Problem is that in P2P .. all Players have to be Syncronized.
And you cant syncronize a ♥♥♥♥ pc with a good one, but you can force the good one to run slower...
So if one Guy on the Server lags around witth 10 fps.... everyone gets slowed down to slow motion ...
Make sure the People you play with have halfway compareable hardware and not 1 of them plaaying on a 2012 videocard or so