Brown's PLME program only accept's students directly from high school. The other half of the med school tend to be non-traditional and older applicants to offset the younger PLMEs. Because Brown's class size is already super small to begin with, the chances are probably pretty low comparably.
Your best shot at getting into med school is being at a school where you go get the best GPA. Unless the school is a HYSPM tier school, it becomes less important where you go. Some med schools like BU actually don't really take any of their undergraduates because they have a pretty terrible premed program.