IIRC NEC requires 20 amp circuits for the kitchen. However the only time I've seen a 5-20R in a residential kitchen is after the electrician got done with mine (he insisted code required the 20 amp receptacles).
It's not required, but it is allowed. And, the only thing you need to do is swap a 5-15 for a 5-20. No other work needs to be done and it's all compliant.