Real world testing comes to the same conversion. 10 % saving in pure city traffic can be expected.

Only stopping for 1.5 hours on red lights over 3 years makes you an super extreme outlier. Now you don't specify the total distance in those 3 years, so perhaps you just don't drive at all, but realistically people drive something like 10'000 km per year, average speed around 50 km/h, time spent driving about 30'000 km / 50 km/h = 600 h. To only get to 1.5 hours at red lights would mean 10 seconds per hour of driving. I hope that makes it clear how unrealistic YOUR number is.