Under certain conditions, screen redraw may be very slow when spell checking in MacDraw Pro 1.5. This can happen when the offscreen buffer is disabled ("Draw directly to screen" option in Preferences is ON). The solution is to turn this option off.
Note: MacDraw Pro 1.5 may disable the offscreen buffer automatically if it needs the RAM to function. This is noted in "About MacDraw Pro": Info.
In this case, making more RAM available to the document will automatically turn the offscreen buffer back on.