I do notice significantly more WOB on my 15 than I do on my 15.5. I have fitted a MK 16 DSV and hoses to my 15, so the hoses are not the reason. Unless you widen the openings from the center section, it will never breathe like a 15.5 or 16.
The canister duration does not surprise me either as there is significantly more sorb and thermal protection in a 15.5/16 canister than in a 15.
Thanks for the link. There are also some really good articles here if you search for "MK 16":
Public STINET (Scientific and Technical Information Network)
At that link, you can find pricelists, parts lists, and a bunch of studies. Pretty cools stuff.
Aloha,
Charlie