There are a number of options you can deactivate to make using Nautilus a faster process. First, click Edit > Preferences, find the tab marked Preview, and click on it. If Show Text in Icons (the first option) is enabled it will preview some of the contents of text documents in their icons. Set this option to Never. Next, there's an option called Show Thumbnails. This option will preview image files as thumbnails. Set this option to Never to further improve the speed of Nautilus browsing. If enabled, the option Preview Sound Files will make it possible to preview sound files without actually opening them. Set this to Never as well. The last option, Count Number of Items, shows how many items are within the folders listed in the directory you're currently browsing. Set this to Never.
If you are still not satisfied with the speed of Nautilus, you could check out some other file managers, such as Rox Filer or Thunar.