I've used SW2015 (SP4.0) for the last two projects that I've worked on, and I must say that this is the most bug ridden version in a long time.  Probably the worst since 2008.  And all kinds of crazy changes to the workflow that are purely nuts.  The graphics are horrid.  Trying to see what is happening in a section thru a solid is a royal pain.  Exploded views are broken (double click no longer works), random changes to settings, return vs. enter total bollocks, can't edit sketch blocks while in an assembly, crashes all the time, and slow as molasses.  I'm going to stick with 2014 for a while.  2015 is too painful.