Medical representative is a very low-level job in US. But if you have achieved good performance in the work, this experience still can attract recruiters. For example, you can write how you survive and thrive in a market with fierce competition from illegal commisions; meanwhile you maintain your ethical integrity by not doing that even your sales and income suffered. The adcom weights more on how you think and how you deal with challenges.
GPA 3.1 is a little low for top15. But most schools don't have strict rules for GPA calculation, so a small difference within 0.2 is not a big issue. The most important thing is to get a 700+ in GMAT. That will almost guarantee you can enter top30.