Have you tried $Translate for date conversion?
USER>write $Translate("Dd.Mm.WwYy","WwYy-Mm-Dd","2015-08-02") 02.08.2015
Stolen from Russian forum and Alexander Koblov.
InterSystems ObjectScript is a scripting language to operate with data using any data model of InterSystems Data Platform (Objects, Relational, Key-Value, Document, Globals) and to develop business logic for serverside applications on InterSystems Data Platform.