Tip originally posted by "edt_oni" on the Steam DG2 forms.
"In the Steam library, right click on Defense Grid 2, select Properties. In the General Tab,
uncheck "Enable the Steam Overlay while in-game".
In the Updates Tab, uncheck "Enable Steam Cloud".
You can also try take Steam Offline.
Try using these setting in the "Set Launch Options" under the General Tab
-skiplauncher -numcores 2 -numjobthreads 2
This reduced game CPU usage from 80% down to 40%"