Thanks for posting this comparison. In terms of sharpness, yes, all three are comparable. However, the colors of the 17-55 and 24-105 are similar, while the 15-85 has a slightly cooler tint. You can clearly see the difference in the "green" shell. Did you use AWB or manually set the white balance?
I did AWB, used off camera flash as well so there is a mixed light source which throws the colors off. For some reason the 15-85 test images all look significantly cooler, albeit more accurate, when taken under tungsten light.