Is it handicapped or not? If so, a couple low and a couple high caps should have an advantage. If not, then I'd think it depends on the couple times a year guys. If they can putt at all, even if just to provide a decent read to the other two, I'd take the team with the scratch. The team of 12-15s should take it, though. If your team was 2 scratches and 2 occasional players, I'd take that in a heartbeat.
I've never heard of not playing with who you want in a scramble.
I'm curious where you work that you have a handful of scratch golfers...