Buckfever is that just a 7" buildup total?
Oxbow that's one hell of a street buildup. At 15" that road is going to last. Do you have bad soils as the reason for the spec?
No, we have generally good soils, and in the valley bottoms there is river rock under everything. We do encounter pretty severe frost though, and our aggregate is pretty cheap relative to other areas of the country as we have plenty of it. Our base is also pit run, not crushed.
Some of our gravel folks here produce a 2" minus, no naturals rejected and all fines included, that is much nicer to work with and you don't have the problem of hiding the 6' plus rock on the edge of a driveway and at the end of a fill.
Without enough base we encounter problems in the spring when the frost comes out of the surface, but the water cannot sink into the ground yet. Usually only about a week or two long period, but I have seen garbage trucks sink through the asphalt and get stuck, pushing mud up through the base to the surface.