The network is ultra secure. but we can definitely shave off some time down to 2 minutes would be way faster.

It would actually quintuple transaction maximum from 400k transactions per day to 400k max every 4 1/2 hours so we would have a daily transaction maximum of 2 million.

now if we consider that we will be cutting off modem users from the network and also people with slow connections it will cause an evolutionary pressure to upgrade, bonus. having that extra time for them does make it hard to overcome the network with a lightning fast propagation time but... if everyone has a gigabit connection then we would be increasing the confirmation security over the same 10 minute time period. the same hashing power in a smaller block time frame, statistical increase in security by the number of confirmations, the greater amount of hashing power will overcome anyone even with only 2 minutes of slack with a 25mbit connection.

and yes the authorization can be done instantaneously for paying for coffees and stuff, and it also makes it hard to do a low cost(sub $10) double spend attack within two minutes, those fast food places better have small lines.