why do large cache files translate to long open times?

for work spaces with very large cache (>5gb), when first opening the work-space it takes a very long time to open the first file.  My understanding of the cache is that it is a locally stored file.  So between my solid state drive, and my 8 core processor, loading local files should be a breeze.  If i have a new or empty workspace, it does not take so long to load.  So what is windchill/ creo doing that causes this to take so long?