15 weeks post-op. Dissolvable staples - when will they dissolve? Is it normal to have them at this stage? (photo)

You should call your surgeon and ask them about that because different stitches are used for different purposes. If you need to remove the stitch, you can clean the area and use a sterlized pair of tweezers. 

Hello, and thank you for your question. (Keep in mind that an in-person consultation is necessary for the best advice.) The appearance of your scars depends on a number of factors---including tension across the incision/scar, genetics, etc. From the day of surgery until approximately 1 year later, your scars will continue to mature (and hopefully improve). Be patient, and follow the instructions of your plastic surgeon. Best of luck!
Matthew A. DelMauro, M.D.