Welcome to GB guguma!
I've experienced similiar problem with vanilla NWN in my old laptop. Though when the problem came up, I was in area which was otherwise rather big resource hog, so I always but the blame on that. Spoilers bellow
For example, at the Chapter one, just outside the temple in City Core there is woman who wants to talk about the Penninsula District. Her dialogue has always been slow to me, as well as almost everybody other's as well who are in City Core, and I have notice that City Core was rather bad resource hog for my old comp.
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Like mr. Holopainen over there!"
- Marco Hietala, the bass player of Nightwish