Copy with mates no longer appears to work on SW2015. I've gone back and forth with SW2014 to verify. I've tried with identical models in both 2014 and 2015, and it seems obvious and clear that it simply doesn't work.
The failure happens on the new "select components" screen of Copy with Mates. Even with a model that is fully defined (and for which Copy with Mates works in SW2014), it simply gives the message "mates to be copied with the selected components are under defined".
Is there any known workaround? Copy with Mates was a very useful feature.