Also, Marriott employs a rolling calendar for determination of elite levels. I qualified for Plat in August based on 75 nights August-to-August.

So if your 15 nights post on Jan 2, it's no biggie.

The only thing I don't know is if a January posting of your 15 nights might actually be beneficial. Would that appear to Marriott as a new Plat qualifying in '08, thus being Plat through early '10? I don't know the answer to that...

Of course, you need to look at your pattern of stays over the course of the past 12 months to make sure the rolling qualification would work for you.