First of all you won't be unhappy with the 15-85, it's a pretty good lens, even wide open. Ok it's not an L lens but then not everyone can afford everything at once, right? I am more than happy with it for the moment on my 7D.
I also kept my 55-250 from my previous camera, as i too cannot afford to buy everything at once. This is a very reasonable lens for the money (<£200) but you have to work within its limitations.
The thing is, you want to be out there taking photos and learning, not waiting and saving for the ultimate lenses. Buy a cheap one and use it, then you'll learn to appreciate the better lenses as you get them. You can always sell on the cheapo lens to another beginner who will be in the same position as we are now.
Having said that, if you can afford it, get the best you can at the time.
Cheers, Sie