for international reasons I do write in English, although I am German too.
I do use the 15mm Sigma for Pentax on a K-5 and K-7, i.e. an APS-C Camera with a crop factor of ca. 1.6. I really love this lens, as it is as sharp as it can be. I would not give it away. I can strongly recommed it. For the price it is a real bargain.