Microsoft Skype for Business Server 2015: January 2018

Microsoft released Skype for Business Server 2015, v6.0.9319.514 - not public.
See description in KB4074701 and contact Microsoft Support to get the download

Skype for Business 2016: January 2018

Microsoft released Skype for Business 2016, v16.0.4639.1001
See description in KB4011623 and download from here x86 or x64

Microsoft Lync 2013 / Skype for Business 2015: January 2018

Microsoft released Lync 2013 / Skype for Business 2015, v15.0.4997.1000
See description in KB4011638 and download from here x86 or x64