I don't see how, even if you were blowing through the missions at 15 minutes or less for each one, that's still 5-6 hours. You wouldn't be keeping up with levels either by bypassing mobs and relying on intermixed bounties and mission xp. That and there's a good 20+ minutes of cutscenes that you have to sit though. I know some people say they're pushing the whole campaign on hard or doing it with other people to make it go faster, but still.