The Intel of 2015 still has a very solid competitor eating into its profits: the Intel of 2010-13. I am typing this on a 2600K I bought in 2011, and I have no intention of upgrading any time soon. I have went from 8 GB of RAM to 16 GB, from a 128 GB SSD to a 480 GB SSD, and I upgraded my monitor setup. But my desktop processor is still more than twice as fast as my 4300U work laptop, which I never worry about being slow. I wouldn't be that surprised if this processor lasts me until 2020, unless it stops working before then.
It can go back much further than that for most people.
My computers that are still in use at least once a week...
2006 - Mac Mini 1.66Ghz Core Duo 2GB of RAM - Apple abandoned it years ago but I installed Windows 7 on it and still runs Chrome and Office well enough for my parents.
2006 - Sony Vaio Core Duo 2GB of RAM - upgraded to Windows 7, used by my son for Office, MineCraft and some simple Flash games.
2008 - Dell Core 2 Duo 2.66Ghz, 4GB of RAM, one of the last 1920x1200 displays, it's fast and runs a complete development stack relatively fast.
2009 - Dell laptop Dual Core Pentium, 4GB of RAM, 500GB hard drive. The battery is crap, and it's heavy, but the screen resolution is 1600x900 and it's good enough for everything I need it for.
2012 - Gateway 3.33Ghz Core i3 6Gb RAM. I don't see any reason for upgrading this for the foreseeable future. It''s mostly used for Plex, occasional personal development projects, and office.