I'm playing the game at like 15 FPS on the lowest setting. That's not good...

What is your PC specs?

but off the top of my head:

update graphic card drivers
shut down anti-viruses
shut down background tasks

Buy an older system.

Apparently Bethesda did all their PC QC testing in 2009, and are waiting until everyone buys an XBOX copy before proceeding to update driver compatibility to accommodate 2011 gear.

Just a second ago, Remi posted an interesting tip: http://www.gamesas.com/index.php?/topic/1257101-pc-fps-input-delay-fix/
Hope it helps.

Model: HP Pavilion dv7 Notebook PC

Processor: Intel? Core? i7-2630QM CPU 2.00 GHz

Installed memory (RAM): 8.00 GB

Graphics card: ATI Mobility Radeon HD 6570 (1 GB)

System type: 64-bit Operating System

Hard drive: 950-ish Gigabytes (900 available)

1600 x 900

I've got lower PC and it runs the game on at least 25 FPS on low settings. You have some PC issue.

I run ultra with worse than that, as far as i can tell.

You may have to humble yourself and play under a lower resolution. Like 1280 x 720.

I remember when old games ran pretty bad on my new PC. You know what helped? Updating Firefox, Players programmes and stuff. It's strange but it definitely helped.