Like any skis, each pair will vary a bit in weight and/or flex so these being similar isn’t that surprising but the FEEL of these skis will be noticeable on the snow.
Like the Volkl Deacon Vs the Deacon Master line, the HRC (or Master) adding ash wood in the core will damp the ski more without effecting weight or flex much. Then there are upgrades in the binding plate and bindings in the HRC which will stiffen underfoot and upgrade precision over the plate/bindings on the R15 W.
You also have the option of going to the Piston Plate in the HRC which would add even more oomph underfoot. The bindings are no longer on a demo track and are screwed down on the plate for a very solid mount.
So you have the following steps in their line R15 W, R15 LTD(70mm underfoot, bit tighter radius with better bindings and upgraded demo plate), HRC with X-Cell demo plate and bindings and finally the HRC Piston Plate with X-Comp bindings.
All are great and just a bit more precise and solid as you move up the line.
Have the narrower GS side cut 180cm WRC with Piston Plate and XComp 16 bindings for myself and love them. Not demanding at all but get more out of them the more you put in them.