True that it's demonstrated not limiting, though I wonder what a court would say if you had been advised that no test pilot had demonstrated a capability beyond X knots and you exceeded that and damaged the aircraft.
I was taught C152 was 12kts, so that tallies with 15mph quoted above. It's a big issue with my home base - runway 01/19, typical wind 240/10-15: it was fine when runway 06/24 was still open...
Tim