I recently ran into some issues compiling an older version of the Unreal 4 game engine, and needed to downgrade my Visual Studio 2015 update 3 to update 2.

During a fresh install, the Visual Studio installer automatically goes out, and downloads the latest updates which was update 3.

After so scouring the web, I found a Microsoft site that shows how to install previous versions via command line, but here is the grid, just in case the site goes away.

Visual Studio 2015 editionWhat to runCommand-line to useWhat setup does
Visual Studio Enterprise (the latest public release)Visual Studio Enterprise with Updates (available fromMy.VisualStudio.com)vs_enterprise.exe Note: The default behavior of this installation offers the most recent optional features and therefore, it does not require any command-line parameters.Visual Studio setup will use the most recent feed.xml and install the most recent files
Visual Studio Enterprise Update 3 (the original Update 3 without any further Update 3-era updates)Visual Studio Enterprise RTM (available from the MSDN Subscriptions download page)vs_enterprise.exe /OverrideFeedURI http://download.microsoft.com/download/6/B/B/6BBD3561-D764-4F39-AB8E-05356A122545/20160628.2/enu/feed.xmlVisual Studio setup will use the feed.xml that was available when Update 3 released
Visual Studio Enterprise Update 2 (the original Update 2, but with updates that pre-date Update 3)Visual Studio Enterprise RTM (available from the MSDN Subscriptions download page)vs_enterprise.exe /OverrideFeedURI http://download.microsoft.com/download/6/B/B/6BBD3561-D764-4F39-AB8E-05356A122545/20160620.2/enu/feed.xmlVisual Studio setup will use the feed.xml that was current before Update 3 released
Visual Studio Enterprise (the original Update 2 without any further Update 2-era updates)Visual Studio Enterprise RTM (available from the MSDN Subscriptions download page)vs_enterprise.exe /OverrideFeedURI http://download.microsoft.com/download/0/6/B/06BB0C5C-C767-4250-91DA-AB463377597E/20160405.3/enu/feed.xmlVisual Studio setup will use the feed.xml that was available when Update 2 released
Visual Studio Enterprise Update 1 (the original Update 1, but with updates that pre-date Update 2)Visual Studio Enterprise RTM (available from the MSDN Subscriptions download page)vs_enterprise.exe /OverrideFeedURI http://download.microsoft.com/download/3/2/A/32A1974F-D236-43C1-8981-97DDCBAEF14A/20160225.3/enu/feed.xmlVisual Studio setup will use the feed.xml that was current before Update 2 released
Visual Studio Enterprise Update 1 (the original Update 1 without any further Update 1-era updates)Visual Studio Enterprise RTM (available from the MSDN Subscriptions download page)vs_enterprise.exe /OverrideFeedURI https://download.microsoft.com/download/3/2/A/32A1974F-D236-43C1-8981-97DDCBAEF14A/20151201.1/enu/feed.xmlVisual Studio setup will use the feed.xml that was available when Update 1 released
Visual Studio Enterprise (the original RTM, but with updates that pre-date Update 1)Visual Studio Enterprise RTM (available from theMSDN Subscriptions download page)vs_enterprise.exe /OverrideFeedURI https://download.microsoft.com/download/3/6/1/36188D5F-479F-4A46-BF55-6AE5928D1EBB/20151102.3/enu/feed.xmlVisual Studio setup will use the feed.xml that was current before Update 1 released
Visual Studio Enterprise (the original RTM with no updates)Visual Studio Enterprise RTM (available from the MSDN Subscriptions download page)vs_enterprise.exe /OverrideFeedURI https://download.microsoft.com/download/5/7/B/57BF5016-E4F0-4EB5-BE27-2BFA87E7723F/20150713.1/enu/feed.xmlVisual Studio setup will use the feed.xml that was available when RTM released

Source: https://msdn.microsoft.com/en-us/library/mt653628.aspx