I know a bunch of people said Ball Save off, but that only serves to screw people and not even given them a chance. I don't think that's a good choice, especially with a mix of newbies and good players, as it's the newbies who will suffer the most. It does very little to shorten the games of the good players, unless they get screwed too on one ball.
Rather, the default ball save times on multiball on Stern games is usually larger than necessary. The way to reduce the very long games is to reduce any multiball ball save as much as possible, and turning it off if possible. Setting difficulty level of the first multiball to a bit harder also shortens games, but often that's not necessary if the ball save is reduced and outlanes are made more difficult.