If the 2015 has any aluminum body panels, these are likely to have the corrosion problem because of Ford's manufacturing process. My 2006 GT had the hood corrosion, but the dealer had the hood refinished after I went to Ford's Customer Service with the issue. Currently my 2011 GT has the problem on the leading edge of the hood, but I have not yet approached the dealer to have it fixed.
I will take a careful look at the 2015 Mustangs, and if they have an aluminum hood, I would insist on at least a 5-year written guarantee specifically for this well known galvanic corrosion problem. Otherwise, I will not buy!
Same for me. At this point, it's the only way that I would EVER consider buying a Ford again.