Symptoms
The memory footprint of the Lync.exe process increases in a stress test when you send or receive a file that's larger than 5 megabyte (MB) in Microsoft Lync 2013 (Microsoft Skype for Business). Additionally, the memory remains increasing although the file transfer is completed or the conversion is closed.
Resolution
To fix this issue, install the March 8, 2016 update (KB3114831) for Lync 2013 (Skype for Business).
Note Lync 2013 was upgraded to Skype for Business in April 2015.