Naeri:
Polygons are polygons, so whether they are in a single element or many does not matter. You can try simplifying the elements to reduce the polygon count (if you go to ArchiCAD Downloads in the Help menu you can download the
PolyCount add-on to see the number of polygons and which elements they come from). If you save the elements as an Object(s), click on the
Options button in the
Save Library Part dialog box and select the
non-editable binary 3D data option, this will create a library part that is large in file size but faster for 3D generation.
You should add a Signature to your Profile (click the Profile button near the top of this page) with your ArchiCAD version and operating system (see mine for an example) for more accurate help in this forum.
David