This book constitutes the refereed proceedings of the 15th International Symposium on Foundations and Practice of Security, FPS 2022, held in Ottawa, ON, Canada, during December 12-14, 2022. The 26 regular and 3 short papers presented in this book were carefully reviewed and selected from 83 submissions. The papers have been organized in the following topical sections: Cryptography; Machine Learning; Cybercrime and Privacy; Physical-layer Security; Blockchain; IoT and Security Protocols; and Short Papers.