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 edition What to run Command-line to use What 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.xml Visual 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.xml Visual 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.xml Visual 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.xml Visual 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.xml Visual 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.xml Visual 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.xml Visual Studio setup will use the feed.xml that was available when RTM released

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