Kill stuff on the first floor as fast as you can. Avoid the "boss" fights. They just slow you down. The fight at the chest is an exception as there are numerous mobs there. Many people have someone higher level pull them through as they can usually kill things much faster. If your group of 2 can't clear the floor in under 5 - 6 minutes (some are as fast as 3 - 4 minutes), you're probably better off with some other mob grind in order to level up. The mobs in Skyreach are not particularly difficult but there are a lot of them and low level toons may not have the skills available to kill them fast.