Dpi;
 

Fed Rules:

1st and 17 on A's 30 yardline. B is guilty of DPI. Step off 15 yards from the previous spot. Is it 1st and 2 or do the sticks move and make it first and 10?

DPI in FED rules is an automatic first down and a 15 yard penalty if you do not go more than half the distance to the goal. In your situation it would be first and 10, not first and 2.

Peace

It seemed strange on the field. It made me think that A would have been better off with a 15 yard penalty that did not result in automatic first down because it was already first down.

It may seem silly, but since it was 1st and 17, team A could accept the automatic 1st down and then refuse the yardage.