15 amp outlets on 20 amp circuit

Nope the 15a receptacles are perfectly legal. You might want to replace them if they are poor quality but that will be apparent if the plugs get hot or fall out.

Thanks Greg.

| My kitchen has a 20 amp appliance circuit--12 ga wire and 20 amp breaker, | but all of the outlets on the circuit are 15 amp outlets. Is this something | I should be concerned about? I.e., should I replace all of the outlets with | 20A?
The 15 amp receptacles, if they are modern UL listed devices, are rated for 20 amps current, including a total of 20 amps between each outlet of duplex devices, and passing 20 amps between the upper and lower screws for passing power through to the next device.
Do be aware that if you want to actually meet current electrical code, the receptacles in the kitchen and bathrooms do need to have the 20 amp outlet configuration (NEMA 5-20R) to allow you to plug in a 20 amp appliance (and you have to have at least 2 separate circuits of them for 40 amps total capacity in the kitchen).

Unless it has changed just this year, you only need 20a outlets if it is the only outlet on the circuit.

It hasn't changed in that regard. You do not need a 5-20R unless it's a single receptacle on a dedicated circuit (one duplex receptacle does not count as a single outlet) in any application. The only time a 5-20R would be required in a kitchen counter area is if it were a really small kitchen and there was only room for one outlet box. A split duplex 5-20R would be used with a 12/4 cable feeding it via a 20-amp, 2-pole GFCI circuit breaker in order to comply with Art. 210.11(C)(1).