The “why spirit” question is the most (and really only to be honest) important question that will be asked on the phone interview and the actual interview/MTC. You have 800 hours of 121 SIC. Give it two more months and you’ll be hearing from legacies. Why do you want to come to spirit over delta? United? American? Southwest? Spirit knows that someone with your profile is very likely to jump ship - you need to convince them you won’t.

If you don’t plan to stay at spirit, then I don’t see why you’d want ti waste 3 months in training. Fly a few more months at the regional and go to a legacy. If you do actually want to stay here, answering that question shouldn’t be too difficult.