"Rob, do you think between my 15 and this 45 i can cover most of the year in the pacific nw?"
I have not done any backpacking in the PNW.
Does your current 15 degree bag zip out to a quilt? If so, I think your 15 degree bag, and the 45 degree bag I recommended would be all you needed.
I have a 25 degree bag, WM Alder MF, and I use it from about 20 degrees to around 45 degrees. At 45 I switch to the bag I recommended.