I second some of the replies above. You need to think from the MBA program's perspective. Why should they take you? Are you going to bring worthwhile discussions? Are you going to succeed after the MBA? Can you handle the MBA curriculum? Top 15 is going to be extremely tough. 16-30 don't like people without post undergraduate experience either.
Do you really want to go to a #100 ranked MBA program? I can tell you why they want to accept you. They want to take your money.
Work 2 years. You will have a much easier time answering "why MBA."