That is correct, I normally drive at 14 over for that reason, School zone excluded and I mainly drive at that speed on highway. I would stay away from 30, 40 MPH zones at 14 over. The passing of a school bus while stopped is equal to a dui fyi.
You were good either way, 15 over is considered a major violation as far as insurance is concerned. Insurance companies also do not run an MVR on all applicants every year due to the expense . They just spot check at random. I am in the insurance business and have been for 20 years.