My personal experience with the junk IRS in my ‘03 Cobra has kept me from seriously considering the 2015 Mustang.
When I took my ‘06 in for the airbag recall, I told them I was looking to upgrade to a ‘13-’14 GT (last of the straight axles).
They told me they had plenty, but could not show them to me because they did not have their airbags fixed. They would have been happy to sell me a new one though. I guess I won’t be looking at Ford dealers when I ready for a newer used Mustang.
I have the 2016. Love it.