How to wire a tandem 120 volt, 2 X 15 amp single pole breaker?
With 14 2 with ground you are limited to a 15 amp breakers as 3phase has stated in earlier post this has been code for many years in the U.S. that's why most outlets in kitchens deal with 12 AWG. If you have 14 awg 15 amp breakers are correct and by putting in a double stuff or tandem you can run a new line to add more outlets or split the existing run to have multiple breakers with the existing runs so 2 appliances or devices won't trip a 15 amp when the next outlet over if fed by the second breaker. Never combine the 2 tandem breakers on the same circuit as this would be a code violation and risk a fire hazard.