Whaaa? EU3 runs like lightning for me, and when a nation forms, it usually means there are actually LESS countries in play (for example when forming Scand you need to more or less annex two countries).
Yes but the more TAGs there are, (i.e the more nations), the more lag as they all have to be checked etc. More nations causes more lag. That's why mods like Magna Mundi are reducing the number of nations.