Hi - sorry to be getting back to you relatively late on this question, but hopefully the topic will be of general interest.
You can take the GMAT the day before a school's deadline, if necessary, so taking it Oct 15 wouldn't be "too late" for any school whose deadline is after Oct 15. However, there is a lot more to the application process than the GMAT -- essays, online application, resume drafting, recommender management, etc. I recommend that people who are working on the GMAT under time pressure allot at least some time every day to finish those other key components as well.

It's hard to do GMAT study and application management in parallel, but if you are applying to, say, Rotman (deadline Nov 22), you want to be working on those essays and resume and recommendation management NOW, while studying. If you get a competitive score on Oct. 15, you'll still have plenty of time to apply.

Hope this helps, and good luck!
Margaret Strother