thanks so much for the info, geezer!
i will start searching for the 16's.
I will be buying a winter tire / wheel / tpms package soon. My research revealed that in the Blizzak WS70 (excellent and popular dedicated winter tire) on the 16's, they are only 0.2" narrower. I am going with the 15's. Those are 1" narrower. Granted, the tire will be poorer in dry road / performance driving with the 15's, but here in northern Maine, I need superior winter snow and ice traction. Narrower tire = better winter "bite". The 16's will have better dry road performance, so there is a trade off.
Some have stated that the 15's will not fit properly on the Titanium since it was equipped with 17's originally. I have spoken with my Ford dealer service manager as well as Tire Rack and found this no be untrue.
The main concern with fitting the smaller wheel is disc brake clearance. the front discs are the same size on the "S" model of the 2012 FF (which comes with the 15's) as they are on the Titanium (which has 17" wheels standard). Now, on the "S", the rear brakes are drum. The Ti, SEL and SE sport have rear discs. BUT, the rear disc is a smaller diameter than the front disc, so no worries! Just stick with OEM tire sizing.
Just my two cents ...
[cheers]