This book constitutes the refereed proceedings of the 15th International Symposium on Search-Based Software Engineering, SSBSE 2023, which took place in San Francisco, CA, USA, during December 8, 2023. The 7 full and 7 short papers included in this book were carefully reviewed and selected from 23 submissions. They focus on formulating various optimization problems in software engineering as search problems, addressing them with search techniques, intending to automate complex software engineering tasks. .