From what I could tell when I was shopping a month ago:
- round button on front door handles for advanced keyless entry on a 2014 means Tech package; this was added as standard on 2015 GTs
- if the headlights on a 2013-2015 have distinct silver-black-silver concentric rings around the bulb housing, that indicates the auto-leveling feature that's part of the tech package
Edit: pre-2016, auto-dimming mirror with Homelink buttons was in the Tech package though I wouldn't rely on that as it's easy to swap in a different mirror.
Thanks everyone, this is all the info I need. Confirmed 2014 has i-active sense safety features and how to confirm.