This volume of the EPTCS contains the proceedings of the 15th international workshop on Qualitative Aspects of Programming Languages and Systems, QAPL 2017, held at April 23, 2017 in Uppsala, Sweden as a satellite event of ETAPS 2017, the 20th European Joint Conferencec on Theory and Practice of Software. The volume contains two invited contributions by Erika Abraham and by Andrea Vandin as well as six technical papers selected by the QAPL 2017 program committee.