Three 15 A receptacles on a 20 A breaker
Yes, that’s fine. The NEC specifically allows multiple 15A receptacles on a 20A branch circuit. You must use 12Ga or larger (if in copper) for all wiring - any 14 and you must use a 15A breaker.
This is an exception to the general rules. You can’t put a single 15A receptacle on a 20A circuit and you can’t do things like putting multiple 20A receptacles on a 30A circuit.