This appears to be close to an unofficial SP2, as it: “… contains all the security and non-security fixes released since the release of Windows 7 SP1 that are suitable for general distribution, up through April 2016.“.
http://catalog.update.microsoft.com/v7/site/Search.aspx?q=3125574 (you may need to use IE for this).
See further details here: https://blogs.technet.microsoft.com/windowsitpro/2016/05/17/simplifying-updates-for-windows-7-and-8-1/ and also here: http://www.zdnet.com/article/microsoft-comes-through-with-rollup-of-updates-and-fixes-for-windows-7/
Even more information from the Premier Field Engineering blog – Windows 7 SP1 and Server 2008 R2 SP1 cumulative roll-up now available at a download location near you! (KB3125574)[/url]
EDIT: direct download links for x86 (http://download.windowsupdate.com/d/msdownload/update/software/updt/2016/05/windows6.1-kb3125574-v4-x86_ba1ff5537312561795cc04db0b02fbb0a74b2cbd.msu) and x64 (http://download.windowsupdate.com/d/msdownload/update/software/updt/2016/05/windows6.1-kb3125574-v4-x64_2dafb1d203c8964239af3048b5dd4b1264cd93b9.msu). From another Penton site post.
The downloaded KBs equate to standalone installers, they can be used to update multiple machines, provided any pre-requisites (like SP1 and the April 2015 Servicing Stack for W7) have been installed.
HTG’s walkthrough for installing the Convenience Rollup.