Cal. SF15 is a hand-winding monopusher movement produced by Stoltz Frères (Angelus) in the 1920s. It was introduced around 1925, replacing the Valjoux movements used by the first Angelus chronographs. Calibre SF210 and SF215 are related.
The movement appears to have a 5-column wheel in some images but a 6-column wheel in others. This could suggest that there was a 2-pusher (6-column) version or that the images are incorrect.