If it was me, I would make sure to check the VIN of the 2017 and see if it was made after August of '17. 2017.5 bikes have the updated transmission from what I understand. If not, I would spend a little extra and get a 2018 with a TFT display and the updated transmission, although I am not sure if those are only on the GSA for now or not.
The 2017 GSA I bought was made in June '17 and does not have the updated transmission or the Hill Assist. Had I known, I may have waited...
Having just bought a 2018, I’m only going to comment from one perspective. The bikes are very similar, but in 2017 BMW made changes to the trans which really smoothed out the shifting. Coming from a 2014, the new one has a much better feel, especially when shifting from N to 1st.
Not sure of such a change would be worth it to you.
Thanks for the replies. I'm actually making more on the money than I'm paying in interest but if I had a zero interest loan that would even better. Plus I get a new bike and can add my own upgrades. So going to run over to the dealer and see what I can get worked out. I'll either have a great 2015 or a new clean slate 2017.