Brian,
Welcome to LQ.
Are you using the Cinnamon version of Linux Mint 17.3?
You may find that using the MATE or Xfce versions will help.
In any event you would probably be better using the latest
Linux Mint 18.1 MATE/Xfce:
https://www.linuxmint.com/release.php?id=28
See if one of those makes an improvement.
Also make sure that your laptop is not overheating and all the vents are clear.