This book constitutes the thoroughly refereed post-workshop proceedings of the 5th International Workshop on Empathic Computing, IWEC 2014, co-loacted with PRICAI 2014, held in Gold Coast, QLD, Australia, in December 2014, as well as the 6th International Workshop on Empathic Computing, IWEC 2015, and the 15th Workshop on Computational Models of Natural Argument, CMNA XV, both co-located with PRIMA 2015, held in Bertinoro, Italy, in October 2015. The 12 papers presented were carefully reviewed and selected from 32 initial submissions. The workshops are going alongside with the PRIMA 2015 Conference and are intended to facilitate active exchange, interaction and comparison of approaches, methods and various ideas in specific areas related to intelligent agent systems and multiagent systems.