That’s frustrating because the desktop version of your graphics card does have recent updates for El Capitan.
A quick google search shows that El Capitan and the NVIDIA GeForce GT 640M 512 MB don’t seem to get along too well under certain circumstances.
Perhaps an email to Nvidia to find out if there is one coming?
Until then 2014 is your best option to just be able to get on with working.
Good luck!