I was wondering the same thing for my D, whether do we need to fill out anything for financial aid by Nov. 1. However, according to Yale's FAQ about financial aid for propective students (
Yale University Financial Aid > Frequently Asked Questions > Billing), this is what stated on their website:
************************************************** ******
What is the deadline for applying for financial aid for prospective students?
There is no deadline for applying for financial aid for prospective students. We recommend that you have your application complete by the suggested submission date. This ensures that Yale will have adequate time to process your application. If you cannot meet the suggested submission date please complete your application a.s.a.p. It is in your best interest to know what your financial aid package will be before May 1 when you need to make your matriculation decision.
************************************************** ******
As of today, I have not filed the CSS for my D yet. However, I think I would need to file it as soon as I can within these few days. So to answer the OP question, I think you should not wait until Dec. 15 if you are applying EA. However, if you missed the Nov. 1 deadline, I think it should be okay. But I don't think you should wait any longer based on the above FAQ from Yale's website.