Generally the introduction of a significant redesign creates a more-than-usual-depreciation reduction in the value of the older design. Often by thousands of dollars. So even if the '16 doesn't knock your socks off when you see it, the best time to buy a '15 is likely in the months after the '16 is introduced and GM is trying to clear the old design off the lots. If you're actually that flexible to wait that long. yes we can wait. we have another year on our xtended warr. on the DTS
Also, that kind of strategy often may leave you with fewer choices as to option combinations (colors, add-on packages, AWD or not, etc) because when they're done making them and trying to clear the lots. . . it is what it is. This may or may not be important to you. that's another 'twist' on the decision - that makes sense also - seems it's all such a 'gamble'
How much additional risk you take on rushing into a significantly re-designed '16 is somewhat dependent on just how thorough a re-design it is. The 2010 was a very large change. I don't know that we know yet how much of a change the '16 really is. Reading 'guesses' the body will change & possible RWD added & V8 (for SRX) but again i'm only a noivce and who knows what the pundents are claiming is correct.
Personally, I love the styling of the '10-15, (me, too)
and suspect I *won't* like the '16 as well on that front, but that remains to be seen. And of course there may be internals reasons (engine, transmission, etc) that make the '16 more interesting to me. There are rumors of a 9-speed transmission, for instance (replacing the current 6-speed).
Some sources are suggesting it could be a 2017 released in mid-2016 so the wait might be longer than you're thinking: