The polar mount should be very near to the centre when aligned to 15W, that is the point of starting there, as above for 15W in your location the polar mount needs to be set at approx 0.8 degrees west of zero.
as long as the polar mount inclination is correct, and you have set the dish declination, by finding 15W as above, tuning the dish through the arc, will enable tou to pick up the sats on it.