@tangofan: suggestion (and maybe this is how you did the model)
- Make only enough geometry to make a piece of the pattern. (i.e. only 15* of the geometry)
- Bring in only one single set of curves that makes the pattern.
- Make that a “Block” so that SW handles it easier.
- Offset the outer surface to the depth you want the cut to be.
- Using the sketch block extrude cut “up to surface”.
- Once the geometry is cut and looks good, pattern the body.
Will probably be much less taxing on your system and easier to export as STEP or IGES… but also try parasolid as that is the best format out of SW.