This book constitutes the refereed proceedings of the 15th International Conference on Logic Programming and Nonmonotonic Reasoning, LPNMR 2019, held in Philadelphia, PA, USA, in June 2019. The 22 full papers and 3 short papers presented in this volume were carefully reviewed and selected from a total of 39 submissions. The papers were organized in topical sections named: applications; argumentation; foundations and complexity; knowledge representation and reasoning; and systems.