I live two blocks form the Rockaway A station, two stops from the Howard Beach/JFK station that hooks you into the Air train. It's at least 30 minutes on an express A to Fulton St, the first stop in Manhattan. Takes me about 45 minutes to get to Penn station from my house, an hour or more with delays. Unsure of what the Air train to LIRR Jamaica then to Penn in Manhattan takes, might be faster then the A depending.

15 minutes to fly from JFK to lower Manhattan is at least a 3x speed up, likely closer to 4-5x.