The 15th International Workshop on Worst-Case Execution time Analysis (WCET 2015) is a satellite workshop of the 27th Euromicro Conference on Real-Time Systems (ECRTS 2015), the premier European venue for presenting research into the broad area of real-time and embedded systems. WCET 2015 is kindly sponsored by TACLe (www.tacle.eu), an European COST-Action on Timing Analysis on Code-Level, FP7 IP Project PROXIMA (www.proxima-project.eu). WCET 2015 is supported by the HiPEAC Network of Excellence (www.hipeac.net).