GFCI rating for Bathroom and Kitchen
15A refers to the receptacles on the front, not the terminals on the back

All 15A receptacles (including xFCI types) made today (and in recent history) are required to support a feed-through rating of 20A -- this means that they can support 20A from one set of screws (LINE for an xFCI) to the other set of screws (LOAD for an xFCI).  As a result, having 15A duplex receptacles on a 20A circuit is A-OK -- you have more than one receptacle there, and pulling a combination of 20A from the two 15A receptacles is OK due to the feed-through rating, so Code permits this.