Through a fork, it can be negotiated down. But whether or not there is consensus support on that is doubtful.
I suggest to you that if you are looking for something with lower block times, just look at available altcoins with somewhat stable value for now.
However, I don't see much of a reason for change at the moment. 10 mins is already extremely fast for an average confirmation compared to how long traditional banking systems take to clear just a simple international or even domestic bank transfer/cheque deposit. There isn't really THAT much of a practical difference between 10 min block times, or 5 min block times.