This volume contains the papers presented at the 15th edition of the International Workshop on Satisfiability Modulo Theories (SMT 2017). The workshop was held on July 22nd and 23rd 2017 in Heidelberg, Germany in association with the 29th International Conference on Computer-Aided Verification (CAV 2017). The SMT workshop is world's premier annual event dedicated to SMT. It is a forum that brings together researchers of SMT, users of SMT technologies, and students. The workshop covers all aspects SMT including new decision procedures, novel applications, implementation techniques, theoretical developments, evaluation methodologies, and case studies. As in previ- ous years of the workshop, we invited three categories of papers: extended abstracts, to describe preliminary works in progress and solicit feedback, original papers, to present original, mature research, and presentation-only papers, to provide additional access to important developments that SMT Workshop attendees may be unaware of.