I was an IT intern at Mac in 1990. I'll always remember that was the summer before Desert Shield because C130s dropped by to pick up all their extra Pegasus engines (used in AV-8B Harriers) for use as spares for Marine birds in the field.
Anyway, at the end of the summer, my boss (who had helped design F-15 components prior to transitioning into IT) set me up with a buddy on the production line for a couple of days of watching 'em build 15s and 18s. I saw a two takeoffs as you described -- I was told that the test pilots did that on just about every first flight.
The F-15 is my favorite fighter of all time. Spent many nights in Germany in the late 1970's admiring their lines as I drove the flight line guarding them.
Was able to see many night-time full-afterburner take-offs...what a beautiful sight!