you'll trip the breaker. It's also unsafe. If your circuit is 20 amps, you can install a 15-amp receptacle, but only if you have multiple receptacles on the same circuit, like the common two-plug ...

In contrast, a 20-amp features an additional horizontal slot, forming a T-shape. This design prevents high-powered devices from being plugged into a 15-amp outlet. Wiring and Circuit Ratings ...