A believe 2015+ are more sensitive to the change to test pipes and more than likely to throw the CEL. Can still try the additional extensions though and see if that works for you.
As for tuner, I haven't done it myself, but if nobody is in your area to directly tune, you can reach out to a few well known tuners (SpecialtyZ, SOHO, Z1, and many others not named Admin Tuning
) and get an e-tune.