Skyrim working slowly

I'm not an expert, but I'm almost positive that Skyrim should be running much faster on our computer, I don't know why it's so slow.

Dell XPS 8300

Intel Core i5-2300 CPU 2.80GHz (it's a quad core I think)

6.00 GB RAM

64-bit

AMD Radeon HD 6459

I am running Skyrim on 800x600.

Antialiasing and Anistropic Filtering are both off, FXAA is on. Everything else is set to default.

I have about 15 fps (7-8 outside, 21-22 inside)

Skyrim