The Voice of O365 follows the Microsoft Lifecyle Update policy.
Current version: Skype for Business 2015 Enterprise MarchJanuary 2018 CU6HF2CU8
Latest version: 
Compatability matrix
...
| Version | Cumulative Update | KB Article |
|---|---|---|
6.0.9319.537  | January 2018 (current) / CU8 | https://support.microsoft.com/kb/4464355 |
| 6.0.9319.534 | July/August 2018 (current)/ CU7 | https://support.microsoft.com/en-gb/help/3061064/updates-for-skype-for-business-server-2015 |
| 6.0.9319.516 | March 2018 2018 / CU6HF2 | https://support.microsoft.com/en-us/help/3061064/updates-for-skype-for-business-server-2015 |
| 6.0.9319.510 | December 2017 / CU6 | http://support.microsoft.com/kb/3061064 |
| 6.0.9319.281 | May 2017 / CU5 | http://support.microsoft.com/kb/4012621 |
| 6.0.9319.277 | February 2017 / CU4HF1 | http://support.microsoft.com/kb/3207506 |
| 6.0.9319.272 | November 2016 / CU4 | http://support.microsoft.com/kb/3199093 |
| 6.0.9319.259 | June 2016 / CU3 | http://support.microsoft.com/kb/3149227 |
| 6.0.9319.235 | March 2016 / CU2 | http://support.microsoft.com/kb/3134260 |
| 6.0.9319.102 | November 2015 / CU1 | http://support.microsoft.com/kb/3097645 |
| 6.0.9319.88 | September 2015 | http://support.microsoft.com/kb/3098601 |
| 6.0.9319.55 | June 2015 | http://support.microsoft.com/kb/3061059 |
| 6.0.9319.0 | RTM | NA |
...