U15 or U-15 may refer to:
Submarines
- , various vessels
- , a submarine of the Austro-Hungarian Navy
University associations
- U15 (German universities), a university association in Germany
- U15 Canada, a university association in Canada
Other uses
- U15 (Berlin U-Bahn), a transit line
- Cubohemioctahedron
- Small nucleolar RNA SNORD15
- Uppland Runic Inscription 15