Ah for some reason I thought you had posted in another thread that you respecced one of your shamans resto and it made things easier.

Aside from that, it just takes more DPS. The more spellpower/haste/crit/etc you have the faster things will die. Practice + DPS is the only deciding factor on a 25 minute run I would think a 25 min run would be easier as a multiboxer than as a group of 5 players because you will be much more well coordinated.