Dose it deserve exceeding over the speed limit?

Sometimes we pass cars in front of us, because they move at around the speed limit, maybe 36 in a 35 zone. As all the drivers know in heart, only driving more than 15 over the speed limit is dangerous and could bring out severe fine, so it becomes a potential rule to drive between 5-15 over the speed limit.

On this Monday night I drove back from Pittsburgh. The traffic condition was so great. There were almost no cars in front of or behind my car. I drove at the fastest speed, 15 over the speed limit. Usually it takes 3 hours from Pittsburgh to State College. This time I thought I could save some time and get home much earlier. The fact is that it took 2h45min driving back home.

It only saved 15 min out of 3 hours. I am wondering whether it deserved exceeding 15 over the speed limit.