Basically there is no pro to the HBAR on this type of rifle, only cons. Cons include its unnecessarily heavy, its heavy and it doenst need to be, it weighs more, and unless i forgot, it is heavy.
The difference in accuracy and noise will be negligable between a 14.5" barrel and a 15" barrel. The primary difference will be velocity. The longer the barrel is (to a point) the higher the velocity. The higher the velocity, the longer ranges ammo will maintain fragmentation velocities.