I can easily recommend the 15-85 on a cropped sensor body. The ability to go from the FF equivalent of 24-136 mm is truly remarkable and a real asset for a walk around lens. You can go from landscape/waterfall shots to include the full portrait range with a single lens. You need light with the lens, but can compensate indoors with a good flash (I used the 580 II). Great combination. Regarding your other lenses, I moved from the 50 mm f/1.8 to the 50 mm f/1.4 and highly recommend the latter over the former. IQ from f/2.8 on is about the same, but better build quality, faster AF and better IQ from f/1.8 to f/2.8 make the upgrade well worth it. I've been tempted several times by the 85 f/1.8 (same build quality as the 50 f/1.4), so I expect that is a very good lens as well. Good luck.