This update enables you to join a meeting without an audio device through the Meeting Join Launcher when you set the Join meeting audio from option under Option > Skype Meetings > Joining conference calls to Skype for Business in Microsoft Skype for Business 2015 (Lync 2013). Additionally, if you accept a meeting invite audio toast, you can also join a meeting without an audio device.
How to get this update
To get this update, install the June 13, 2017, security update (KB3191939) for Skype for Business 2015 (Lync 2013).
Note Lync 2013 was upgraded to Skype for Business in April 2015.