As an old newsie let’s take a look at how you are doing. 150 papers in 2 hours 45 minutes now or 165 minutes. That’s 165/150=1.1 papers per minute or 66 seconds per paper. Your goal is two hours or 120 minutes 120/150=.8 papers per minute or 48 seconds per paper. So you are faced with improving each delivery by 18 seconds is all. That sounds easy enough until you figure that’s about a 25% improvement over what you now feel is giving it your best effort.
In this type of problem you have to take into account the time you expend that is fixed and can’t be changed easily things like riding your bike from point A to point B and things that can be improved like memory vs list etc. To get 25% out of the total time by shortening or eliminating these little short times will help but you will need a lot of them to get to 18 seconds per house.
Then there is the option of route modification. We don’t know your route so that’s hard to help with. The US postal service in city delivery gives each worker a vehicle but they do their delivery mostly on foot. They carefully choose a starting point and have mail sorted for a small area where their foot route starts and ends at the same point or close to it. They then move and reload the next section into a hand carry bag and repeat. If your route is stretched out and you park grab a series of papers ending a great distance from your bike having to run back only to retrace those steps on the bike I doubt you will save much time. Getting a good map and reviewing it thinking about your foot speed vs bike speed you could model your 150 stops and on paper find the savings in time and then try it out and see how badly it beats you up.
IMHO I think you are doing very well at the 1.1 papers per minute and maybe set a goal for 1.0 per minute. For now I would start at 4:15 am.