From comments in this forum it's obvious that the 2015 version has many problems on the Mac.  In many cases (mine included) it simply won't run.  Researching the troubleshooting section (Post 9036 and iquestion 15116) herein suggests that deleting all old version references including those in Library and Users folders -- that doesn't work either.  Many users are citing urgent needs.  In my case I'm in the middle of a new home construction and just as we are laying out all of the concrete forms -- at the worst possible time -- I suddenly have no way to open drawings that took 6 months to develop.   Until the 2015 problems are sorted out PLEASE PLEASE PLEASE let us use the old version.