This book constitutes the refereed proceedings of the 15th International Conference on ICT Innovations 2023. Learning: Humans, Theory, Machines, and Data, ICT Innovations 2023, held in Ohrid, North Macedonia during September 24-26, 2023. The 17 full papers included in this book were carefully reviewed and selected from 52 submissions. They are organized in sections by topics as follows: AI and natural language processing; bioinformatics; dew computing; e-learning and e-services; image processing; network science; theoretical informatics.