As far as I can see, the main locations don't have any loading screens per se. As soon as you come close to a new loading-area, you will see the small rotating icon in the bottom right corner. If you now move too fast further into the loading zone and the game is not ready yet, it shows you a loading screen. The same with houses: If the interior would load faster, it wouldn't even fade to black. The gameworld has various of such "loading puffer" zones, which look like a big room, where you have to go through doors or walkways in which the game loads parts of the next area behind it. Few examples for this are the area from Flotsam town to forest or that military camp in chapter 2 to the battle field, various cave entrances are build in a similar way as well (so you don't see many objects in the distance, if at all).
That's why I stop moving around for a bit when I see the loading icon. Game is more fluent then and seems to load faster.