From the 2002 NEC, 404.14 (A), Alternating Current General-Use Snap Switch. A form of general-use snap switch suitable for use on ac circuits for controlling the following:
(1) Resistive and inductive loads, including electric-discharge lamps, not exceeding the ampere rating of the switch at the voltage involved.

Finally, my question. I take that to mean that I can use a switch rated at 15 amperes on a circuit protected by a 20 amp OCPD as long as the load does not exceed 15 amps, correct?