Hi all. I enjoy photography and am an avid amateur. I am interested in picking up the canon 17-55 mm lens as a walk around lens. I have a number of lens including the canon 10-22mm and canon 15-85mm. I recently purchased the Tamron 16-300mm lens for when I travel ( do travel a lot and like the Tamron and my canon 50 mm 1.4) My question is am I making an upgrade with picking up a second hand canon17-55mm, and selling the canon 15-85? Seems like a great addition, with the better low light ability and shallow depth of field with the f2.8, not to mention the better glass with the canon 17-55mm. Thanks in advance.