This proceedings constitutes the refereed post-conference proceedings of the 15th International Conference on Simulation Tools and Techniques, SIMUTools 2023, held in Seville, Spain, in December 2023. The 23 revised full papers were carefully selected from 58 submissions. The papers focus on various areas such as Simulation Tools and Methods; Artificial Intelligence and Simulation; Transportation and Logistics; Medical Sciences; and Network Simulations.