I think that its lame that people leave warzones at the slightest hint that their team is losing, and then can join another warzone right away. Sometimes they'll end up back in the same warzone and then leave again, increasing the time the team is shorthanded. Also, usually when one person leaves, multiple people do which means you pretty much lost the warzone right there.
15-30 min debuff would probably be fine.
If you end up on a terrible team then tough luck. Take the loss like a man or try and do something about it.