[Dridzt]

Excessively large saved variables and missing files both contribute to slow loading times.

The first needs no further explanation I think.

As for the second you can get an idea by looking at World of Warcraft\Logs\FrameXML.log

It's normal to have "some" entries there (it's not the same as lua errors)
but if you have too many lines with "unable to load such and such" file these add alot of loading time.

This is usually a problem with improper setup of dis-embedded libraries or occasionally obsolete files that the author didn't bother removing from the .toc of their addon.

Game tries to find each of these files and also writes the error to framexml.log both of which add to loading times.