Use this python script to perform an automatet vertical tilt correction on the current view.
Or use it this way to correct the view of a viewport:
Right click at the viewport.
Edit camera
Run the script
exit edit mode
xAngleR, yAngleR, zAngleR, offsetPt = vs.GetView()
vs.SetView(-90, yAngleR, 0, offsetPt[0], offsetPt[1], offsetPt[2])
Don't forget to set the script-language to python in the script editor.