Hello,
Kindly disable hardware acceleration in AutoCAD, And follow the below mentioned steps :
1) Open Parallels Desktop.Do not start the Windows Operating System.
2) On the menu bar click on Parallels Desktop => click on preference => Memory.
3) Manually change the Memory to 1000 MB => Click on OK.
4) On on the Menu bar click on Virtual Machine => Configure => Memory.
5) Manually Change the Memory to 1000 Mb => Click ok
6) Launch Parallels ( do not start windows ) => Go to Configure => Smart Mount => disable the Smart Mount option
Please check if the performance has improved.
If not then please follow the below mentioned steps this could resolve the issue.
1) Launch Parallels Desktop.Do not Start the Windows Virtual Machine.
2) Open Configure => click on CPU => Manually change the number of CPUs to 1.
3) Restart the Mac.