All movies have metadata by XBMC, , well I use https://mediacompanion.codeplex.com/ for this..

All the nfo and tbn are already on the computer...

In the settings I disabled everything for metadata extraction except the XBMC checkbox.

To add 400 Movies takes roughly 6 hours. XBMC, Plex, TVersity, etc use 2 or 3 Minutes to add this amount of local data.
I now delete all db files.. everything is empty in the program..
I now add 400 DIFFERENT movies.. takes roughly 6 hours again... as expected..

Now I add the first 400 Movies to them.. it now takes 12 hours !! Why?? Well, obviously 6+6 = 12.., but why would the updating metadata
do the first 400 again?? I selected the option only update new files..

Now I add anouther 400 Movies.. 18 hours!!! ...
Now I add 1 new movie.. 18hours + 10minutes..
ehem.. so each new movie EVERYTHING is scanned again and again`?? Even with the option NOT to scan everything but only new files..

even if fixed, why does it takes so many hours for local metadata...

so, many things are wrong with this software performance wise..

It's the best media server on the market, and I tested them all.. but on the performance you really should fix some major issues here.