This link provides valuable planning information for ensuring IE is kept up to date for workstation and server security requirements.  It is always a best practice to be on latest IE version and to stay patched fully, so as to benefit from better protection in latest releases. 

http://blogs.msdn.com/b/ie/archive/2014/08/07/stay-up-to-date-with-internet-explorer.aspx

After January 12, 2016, only the most recent version of Internet Explorer available for a supported operating system will receive technical support and security updates. For example, customers using Internet Explorer 8, Internet Explorer 9, or Internet Explorer 10 on Windows 7 SP1 should migrate to Internet Explorer 11 to continue receiving security updates and technical support. For more details regarding support timelines on Windows and Windows Embedded, see the Microsoft Support Lifecycle site.

Beginning January 12, 2016, the following operating systems and browser version combinations will be supported:

Windows Vista SP2 Internet Explorer 9
Windows Server 2008 SP2 Internet Explorer 9
Windows 7 SP1 Internet Explorer 11
Windows Server 2008 R2 SP1 Internet Explorer 11
Windows 8.1 Internet Explorer 11
Windows Server 2012 Internet Explorer 10
Windows Server 2012 R2 Internet Explorer 11