I can confirm Heavensward dx11 client crashes on MSI R9 390x gaming 8g with 15.15 drivers as well as the 15.20 drivers that came with the CD. The crash is easily reproducible on a 2 or 3 monitor setup. The main display has the game running on it. The 2nd display has a youtube video playing. The playback causes the game to freeze within 30 seconds of beginning video playback. None of the settings for Video in Catalyst Control Center make a difference. Game is running in Borderless Windowed mode on max settings.
This issue is not present on systems with 290x running the 14.12 omega drivers. The issue also does not appear when running on the older dx9 client.
Issue seems to be present with the R9 300 series drivers.
If there was a way to rollback to the omega 14.12 with the 300 series, that would probably fix many of these random crash issues. I also suspect that if the 14.12 drivers could install on a system with the 390x the issues would be resolved.