Mebane 5.7 million
McDaniel 3.6 million
Carpenter (expected 3 million)
Zach Miller 3 million

That's 15.3m there. Figures taken from Davis Hsu's cap 2015 breakdown.

This still allows for:

Extending Wilson
Extending Sweezy
Extending Wagner
Resigning Kearse
Resigning Moeaki
Expected sign of UFA DT (2m)

It's not as far fetched as one might assume. It would require drafting replacements for Mebane, Carpenter and Miller. One could also not sign a UFA DT (since Suh would be part of that), and keep Miller and find 1m elsewhere (perhaps lose Kearse).

Thing is, at #31, we should easily be able to replace Carpenter. There will be great day one starter OG talent available at that point. Additionally, at #62, we'll be in a great position to draft a run stuffer specialist to replace Mebane. This kind of move really isn't as far fetched as we might think it