If you're using a 15x1 needle it will be too short. The 20x1 is longer. Compare the needle you are using to the one that was in it, and you'll see. The numbers on the needle you are using is not the needle system number, but the needle size in diameter.
The 20x1 and 15x1 are the same except for the length. You can short seat a 15x1 so it sits out as long as the 20x1's do and it will work.
That is what I do on my two machines that use the 20x1 needles. Both made by New Home.
Joe