There is a simple reason why you are slower than others who do the round. Its inexperience not of the work, although that will have some effect, but of the duty.
Once you have done a few months on the same duty/duties you speed up. Why.
You don't have to think where the next address is - you go straight to it without thinking.
You don't have to think - where the letterbox is on strange addressees.
If you back streets you know without thinking the best way to do it.
You know the most effective way of bagging up and can take into account days when you have large numbers of packets for one.
It might not be a lot of time saved for each address - but at only 1 or 2 seconds on my delivery it amounts to nearly 30 minutes. On a busy day it will be a lot more.