SM U-15 or U-XV was a U-10-class submarine or U-boat of the Austro-Hungarian Navy (German: Kaiserliche und Königliche Kriegsmarine or K.u.K. Kriegsmarine) 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 8,000 gross register tons (GRT).