It honestly depends. If the 15K hour guy had been flying a B1900 for most of that time and the 1200 hour guy got into the CRJ at 300 hours with some East Coast or Midwest commuter swapping legs and that is all he has been flying since, I would probably hire the 1200 hour guy. I would need to get them both in for an interview and see if the egos and arrogance are in check. Either one of them is going to have to be retrained, but if one already knows everything, then he does not need the job you spoke of as it's a learning environment.
I honestly do not feel as though there would be much difference in a guy that has changed a tranny 50 or 1000 times. I cahnge the own oil in my car, and the 1st couple of times I did it, I remember having the book out checking replacement quanities, torque settings, etc. When I do it now, it's all natural and I can do it with my eyes closed. Maybe that is not the smartest thing to do, but I guess it is all just a matter of opinion. For me, I guess I have no problem with cutting a guy a break, as good people tend not to forget that, and loyality trumps when push comes to shove. In aviation, if you can send someone to school and they do well, I have no problem with them flying my family, as long as I don't have to teach them to fly. With a 1200 hours guy, I'd put him in the right seat and he'll be swinging that gear for 100 to 150 hours. During that time, any empty legs he would get from the right seat as well, but he'd actually get to fly. After that, he fly from the right seat for 10-20 legs with Pax on board. Once those 10-20 legs are complete, I'd give him a few empty legs with no pax on board in the left seat in order to get use to the yoke to tiller and tiller to yoke transition. Once he is good there, then it's business as usual, swapping seats and legs. The trouble with some pilots, young and old, low time and high time, they think they are ready for more than they are getting. A pilot new to jets needs to sit in that right seat for a little while and just absorb what he sees. I was amazed at how much I learned about flying by not flying. Some guys get pissed off cause they are in the right seat, and if some 1200 hour guy I jsut hired so much as peeps about his current roll, then he needs a "Come to Jesus" meeting.