Good morning Eddy.
I agree at the outset it sounds odd.
The NEC allows multiple 15 amp receptacles on 15 or 20 amp branch circuits.
If it is a circuit with just a single receptacle than you would need a 20 amp receptacle on a 20 amp circuit.
The thing to keep in mind is that a listed 15 amp receptacle is designed and tested to be used on a 20 amp circuit.
