My 20A appliance loop in the kitchen has 15A receptacles because, heyyyyyyy, you're not really going to draw 20A out of these right? Those 2000 watt appliances don't go on a 20A loop that can pass 2200 watts... I use a Breville 1800W toaster oven drawing over 16A through one receptacle. One 15A receptacle on 20A wiring.
Most 15A receptacles are rated for 20A pass-through, so they should be perfectly fine to use on a 20A line. The only time you should need a 20A receptacle is if you have a single device with a 20A T-shape plug.