Recessed chin/ jaw line, can a genioplasty correct by 15-20mm ? (photos)

Thank you for your pictures. To get the degree of advancement that you may require it appears that the attention should be aimed towards your jaw. In my opinion, it appears that you have a severe recession of your lower jaw. I would recommend visitation with an orthodontist and an oral and maxofacial surgeon for evaluation to improve your profile. Best wishes.

You are correct in that a sliding genioplasty is an essential part of your chin correction but would not be enough on its own. (12 to 14mms at best) You would need to add a chin implant overlay in front of the sliding genioplasty to get the maximum chin projection.