SM U-15 or U-XV was a U-10-class submarine or U-boat of the Austro-Hungarian Navy () during World War I. U-15 was constructed in Germany and shipped by rail to Pola where she was assembled and launched in April 1915. She was commissioned in October 1915. U-15 was the most successful boat of the U-10 class, sinking six ships totaling more than . The boat survived the war and was handed over to Italy as a war reparation and scrapped in 1920.