This book constitutes the refereed proceedings of the 15th International Symposium on Experimental Algorithms, SEA 2016, held in St. Petersburg, Russia, in June 2016. The 25 revised full papers presented were carefully reviewed and selected from 54 submissions. The main theme of the symposium is the role of experimentation and of algorithm engineering techniques in the design and evaluation of algorithms and data structures. SEA covers a wide range of topics in experimental algorithmics, bringing together researchers from algorithm engineering, mathematical programming, and combinatorial optimization communities.