It's about Feats. Look on the Feats tab, you have to check off everything except PVE feats. You get so much prowess for killing mobs. It's best to have at least 3 people in a spawn. Or 2 people and a ALT. The speed of the mob spawning depends on how many players are at that spawn. We found that as long as you have 3 players they will spawn faster than with two.