The main problem here, that ArchiCAD saves each dot from vector fill as separate dot. Because you are covering big area with dot fill you are getting big file and your PDF application might simple not render all these dots.
The solution to similar problem - try to avoid using vector fills for large areas (it mostly happens for site plans). Use symbol fills and photo fills - then it will be saved into PDF as fill. File will be smaller and PDF viewer would be able to render it better.
