Rokinon 14mm f/2.8 vs EF-S 15-85mm f/3.5-5.6

I currently have a Canon 15-85mm that I use on my 600D/T3i; I'm looking at getting into night sky photography, and the (admittedly few) attempts I've made thus far have left me disappointed.

I find I have to keep my camera at ISO 6400 just to get a decent exposure without star trails, and I'm wondering if the extra 2/3 stop of the Rokinon is worth picking that lens up? Does anyone have any experience/input? Or recommendations on how to keep the sensor noise down?

I know the Canon 14mm L would be a far "better" lens, but it's simply out of my price range.

Edit: Upon further thought, I suppose another option is the Rokinon 8mm f/3.5 Fisheye which would allow almost double the exposure time before trails appear, so please offer thoughts on that, too.

A lot of people blend multiple shots to collect more photons without running into star trails. Are you at a dark sky area? Do you manual focus on 10x Live view (pick a very bright star)? I don't think that the difference of 2/3 stop is really important here. You can get a decent start on the 15-85 wide open, and when you want something wider, go for the SamBowRokinon 8mm fisheye, which is also f/3.5. I do have the Samyang 14mm f/2.8, it is very good at 2.8 for APSC, but really should be used at f/4 for maximum FF corner sharpness and minimum coma. Tip: if you face south, you get more trailing than if you face north. You might find that oval stars are fine if you are wanting the general effect and not 100% magnification.

I tried to get some meteor photos last night with my Samyang 14mm and 5D3. It was the first time that I photographed stars and I did not notice any star trails even at 30 seconds.

Those are actually quite impressive.

I went back to my previous photos, and played around with image averaging to reduce some of the noise, and I think the biggest problem for me was light pollution.  I'll be sure to get some more experience in before I go out and buy anything.