Swap out 20amp breaker with a 15amp for kitchen circuit
Not a code expert or have any quote here...but I think code might require 20 amp circuits in kitchens, since it's expected to have a lot of extra power draw there.

However, what you have now is a fire safety issue.  Far better off with the 15 amp breaker than having wires too small on a 20 amp breaker.

The ideal solution would, of course, be to replace all the wires with 12 gauge.