If your goal is PI/Government, both Chicago and Duke have Loan Repayment Assistance Programs, which would allow you to enter directly into PI/Government Work. UChicago's seems a little more generous (IIRC from the spiel they gave at admitted students weekend they'll pay 100% of your required payments for ten years, after which your debt is forgiven by the government.)
It would be a good idea to get into contact with both UChicago and Duke about these programs if PI is your ultimate goal and to do reasearch into the Income Based Repayment plan and Public Service Loan Forgiveness offered by the Federal Government. Also, I know some loan program deadlines have come up/passed so that may be an issue you want to raise with UChicago about whether your debt will be dischargeable from this first year under the LRAP plan they mention.
Here's UChicago's info: http://www.law.uchicago.edu/financialaid/LRAP
Here's Duke's: https://law.duke.edu/admis/financial/lrap/
If you're going into Big Law and have connections in New York and Chicago, Duke would open up New York but not Chicago nearly as much. UChicago would probably also offer more connections to the Twin Cities due to location, but that's just conjecture on my part. What it boils down to is the $15k at 7% interest worth a better chance of Chicago to you if you go big law. (IMO this would be worth it)
Edited to reflect you're new COA numbers.