I bought my 2014 Monogram used BUT this was a year ago, and the car had only been owned for about 9 months before the dealer had it. It was in impeccable shape - low mileage - and actually already had the Perrin exhaust installed. I figure given the timing, there's a reason he owned for all of 9 months.
It was significantly cheaper than a 2015, babied by the former owner, and a no-brainer for me. The only concern is yes, it's an AT and not an MT, which I was previously looking at, but I went ahead and test drove it and honestly fell in love with the paddles. Sure, they're not going to be as fast as a double-clutch Audi or anything like that, but given that I often drive in bumper to bumper SF Bay Area commute traffic, it IS nice to very occasionally be able to put it into automatic and ignore it (though 99.9999999% of the time, I never take it out of manual).
For me, it was worth having a little bit of miles on it to be picking up a car with all the Monogram features AND an aftermarket performance exhaust for less money than a new 2015, but I got very lucky and that's not always the case.
Buying used isn't always bad. Buying new isn't always good. In the end, do your research and your homework and weigh the pros and cons of both the cars you're looking at and decide which one you really want and what may cost you more in the long run. Sometimes, saving a little money now means dropping more money into it later as you find things you may not like or may go wrong. Choose wisely, and buyer beware.
Only you can really know which one is the right one for you.