Am I looking at jail time if I am on my third offense drunk driving and I blew a .15?

Quite possibly. A third offense is a felony in Michigan. Hire local counsel asap.

It is up to the judge. A third offense can be charged as a felony. Even if not charged as a felony, there is a substantial risk of imprisonment, given that past probation have failed to deter the illegal conduct. A .15 reading is fairly high, which could cause judges to want to jail you. Get good representation right away.