JHU will not be a top 15 school after accreditation. Not only because there's a tremendous amount of competition from equally or more reputable schools, but because it takes time to build relationships with employers to recruit on campus, it takes time to build a strong faculty, it takes time to come up with a strong curriculum, it takes time to attract top students. Even after JHU has itself established as a bschool, it takes time for people to recognize its quality, which is a determining factor in rankings.
JHU has a great med school, but it does not necessarily translates into a good healthcare focused MBA program. A school can't just ride its undergrad reputation for graduate school rankings. Case and point, ivy league school rankings in engineering.
If you are interested in healthcare management, Duke-Fuqua has arguably the best helathcare management program in the world and it's a top 15 school.
Thank you so much!