I don't have start/stop on my Ghibli. I think its only on the Diesel. The general impression I get is that FCA only fit it if its going to make a difference to some emissions band or other.
I did have it on the Giulietta, which is probably the same system. It was very dependent on outside temperature as well as the state of the battery. Once the outside temp dropped below 5C it pretty much never activated on its own. It also seemed to only look at the start of the journey and not reassess, well not in the 15-20 minutes of my commute. I did find a trick though, which was the result of an embarrassing stall at a set of lights trying to set off in 5th. If you let the engine warm up on the first part of your trip, then turn it off and on at a suitable point, it would function normally for the rest of the journey. I got so that I'd belt along the straight away from our village. Turn the engine off and on at the first set of lights. The start/stop would then work for the trip into the city.