If you think you have a good hard drive then try de-fragmenting it (except if it's an SSD, you DON'T want to de-fragment an SSD!).
Divinity uses quite a lot of files so if you're HDD is quite active, this can help a lot.
Also, be sure to have enough free hard drive space and a large system swap file which should also be de-fragmented (single blob).
Still, this game does have some quite long start-up loading times. So, if you ever get your hand on an SSD, it could be a good idea to put the game files on it.