C150 75-80kts
C152 105kts!
Hmm, I flew both for my PPL 27 years ago, owned my own C150 in the mid-80s, still fly a friend's from time to time (I currently own a Sundowner), and also rented extensively before buying my own aircraft.
The C150 is not quite that slow, and the C152 is not quite that fast!!! It is quite reasonable to expect 100 mph out of a 150 (which is about 87 knots), and maybe 95-100 knots from a 152. FWIW I typically show about 105 indicated on the Sundowner. I can coax it up to about 120 true at higher altitudes though.
Mind you this is for aircraft in good condition. Clapped-out school/rental aircraft may differ...more likely on the low side!