>>>Graphics card?

Could be... Not sure.
Have you tried to reset AutoCAD? If no, you can try, but I'd recommend you to backup
~/Library/Application Support/Autodesk/roaming/AutoCAD 2015
and
~/Library/Application Support/Autodesk/local/AutoCAD 2015
folders in order to be able to revert everything back, or at least to restore your customisations for commands and menus from
~/Library/Application Support/Autodesk/roaming/AutoCAD 2015/R20.0/enu/Support
Plot Styles from
~/Library/Application Support/Autodesk/roaming/AutoCAD 2015/R20.0/enu/Plotters/Plot Styles
Templates from
~/Library/Application Support/Autodesk/local/AutoCAD 2015/R20.0/enu/Template
and Content libraries from
~/Library/Application Support/Autodesk/local/AutoCAD 2015/R20.0/enu/Support/ToolPalette

Maxim