First, you are not saying which version we are talking about. I assume FSX, but it doesn't hurt being more specific. Also, you don't say anything about your system, so we can't have an idea of it. And, you don't say anything about your settings, and that doesn't help either.
Frame rates, as everyone noticed, should be about the same than FSX default OHare. The single thing that can slow it down the most, it's the only thing that it's not part of the scenery: AI addon packages. If you have something like UT with AI at 100%, since our OHare has all real world parking stands available, it can attract an huge number or AI airplanes and, it those are not made with the utmost care to fps optimization (something that not all AI packages offers), you will have a slowdown, although I still haven't seen anyone reporting as low as 2-3 fps.