Buying a mustang.. advice?

I am looking to buy a used mustang, I am thinking probably an ecoboost 2015 or maybe something older. The problem is my budget is around 20k so I am trying to find one with at least like 15-20 thousand miles, so that it will be in my price range. Do you think I should go with the 2015 or do you think I would be able to find an older one that I could customize somewhat and get more for my money. Thanks for your time!