The 15% off applies only bookings with the rate code HB for B&B and HD for DBB from the Leisure Break Brochure. It does not have to be booked through the Shareholder Line. I usually book online at hilton.com and in the comments section put " Shareholder less 15% discount" and it works every time but make sure you choose the room code!! I usually also put in "HHonors Diamond allocate Best Avail Room" and this also rarely fails.

Cheers

Alan