Yes, you can deduct adoption expenses incurred in both 2015 and 2016 for an adoption finalized in 2016.

TurboTax makes this clear on the screen entitled "Credit for Adoption Expenses" when it says "Paid adoption expenses in 2015 or 2016". Later, during the Adoption Credit interview, TurboTax will ask you fo the 2015 expenses on one screen, and the 2016 expenses on the next screen.

This is in line with what the IRS permits – see the IRS webpage on Topic 607.