Greetings,

Yes, 15 amp receptacles be used in a 20 amp circuit. The idea is that
the plug shape will prevent overloading the receptacle. The 20 amp
breaker will prevent gross overloading of the 15 amp receptacle if
someone plugs one of those ghastly power-strips in. You can use 15 amp
switches for lights. Use 20 amp switches for everything else. The
full rules are actually slightly more complex than this but follow
these simple guidelines and I don't think you'll run into any problems.
I am also sure you are aware not to use 14 awg wire in your 20 amp
circuit even if you have 15 amp switches and receptacles.

Hope this helps,
William