In the video, I do see a lot of basenji traits, but who know... some mixes look like nothing they are really related to. Some basenjis, espec mixes, can be quite large.
Sometimes extreme hunger can be from hormones (thyroid even) or cancer.. At 15, not sure if knowing makes much difference. However, there are some meds to make him feel better and up to walking, which certainly would improve his quality of life.