Have one, like it, wouldn't buy a carbon one because I don't want to have to look after a carbon bike (and don't think it would make sense for me as a commuter) I think all the 2015's are carbon, but could be wrong.
Also have a Synapse with drops, hadn't used drops with hoods before, took a little time to get used to braking, but am equally at home on it.
Should be a fair number of second hand Sirrus around, if you want flats it's a good choice. I'm about to put bar ends on mine, I think it needs them if you are doing much distance, all the new ones now come with them.