Wow... why is this so controversial?
Like the anon who said:
"Don't listen to him unless you want to burn your house down. "
People just make this bold, blanket, statements and think that they are doing the world some good. You're not, you're just being ignorant.
CLEARLY multiple people who KNOW have provided the clear answer. Yes, you CAN put a 15 amp outlet on a 20 amp circuit AS LONG AS that outlet is not the ONLY outlet on the circuit.
Yes, you can, yes, you can.. you can... can.
People have pasted code, remarks, and in-depth technical explanations on why it is how it is. Anyone else who'd like to post some "my daddy taught me", unfounded, nonsense should take another look at their professional choices.. because they're clearly not ready for the "rules and laws" system we have in place here in the U.S.
You can put 15amp outlets on a 20amp circuit as long as its not the only outlet on the circuit... Yes, you can, yes, you can.. you can... can. Positive, affirmative, yes, go, do it, go...