Proceedings of the 15th Workshop on Qualitative Aspects of Programming Languages and Systems April 23, 2017, Uppsala. E.P. de Vink & H. Wiklicky (eds.) This EPTCS volume contains the proceedings of the fifteenth Workshop on Quantitative Aspects of Programming Languages and Systems (QAPL 2017) held in Uppsala, Sweden, on Sunday 23 April 2017. QAPL 2017 was a satellite event of the European Joint Conferences on Theory and Practice of Software (ETAPS 2017). The central theme of the QAPL workshops is that of quantitative aspects of computation. These aspects are related to the use of physical quantities (storage space, time, bandwidth, etc.) as well as mathematical quantities (e.g. probability and measures for reliability, security and trust), and play an important (sometimes essential) role in characterising the behaviour and determining the properties of systems. Quantities are also central to the definition of both the model of systems (architecture, language design, semantics) and the methodologies and tools for the analysis and verification of system properties. The aim of the QAPL workshops is to discuss the explicit use of quantitative information such as time and probabilities either directly in the model or as a tool for the analysis of systems.