A "15-sided" shape is known as a pentadecagon. This polygon has 15 straight edges and 15 vertices. Each internal angle in a regular pentadecagon measures 156 degrees, and the sum of all internal angles is 2,340 degrees. Pentadecagons can be found in various mathematical studies and are often used in geometry to explore properties of polygons. They can be regular, where all sides and angles are equal, or irregular, where the sides and angles vary. Understanding pentadecagons helps in the study of more complex geometric shapes and their applications.