Stable versions of FairSoft "jul15" and FairRoot "v-15.07" have been released. Source code can be downloaded as a tar-ball from GitHub: jul15 and v-15.07.
As a reference for upcoming R3BRoot Development Workshop, next version of R3BRoot (July 2015) will be compatible with the mentioned releases. Installation instructions can be found here.
Note: ROOT 6 option in FairSoft is meant for testing purpose only. The releases were not tested with gcc 5.1