Without posting a pipe flow rate and friction calculator here, "no matter what the distance" [and one may assume you mean the head as well] is incorrect. Unless you can find a grinder pump that outputs 300 or 400 PSI, you will need INTERMEDIATE pump stations on long runs and high heads in order to preserve your belief in 1.5" pipe. I hope you know that at a certain point in length and head, a pump outputting even 500 psi will allow a little pee type stream to exit the pipe. I don't think your sewage or tie in would be particularly successful with your theory.
What does that mean, increasing the size of the line you are connecting to at the city?
Good to see you didnt go back to the PSI to open a door issue.
The e/one grinder pumps will pump horizontal through a 1.5" pipe for over 4,000 ft. If it had to go further the answer would never be increasing the size of the forced main on the customers property.......it would require a bigger pump and the bigger pump would have a larger outlet. You simply never just increase the customers service line.
It means the city would need increase the size of their line to match the size of your line. You'll never see a 2 or 3" lateral line for the typical property...those are the size lines you find out in the main lines the city uses.
The door under water is exactly true. Until the pressure equalizes on both sides of the door the larger door will be much harder to open than the smaller one because theirs more surface area for the pressure to act on.
It really wouldn't be a problem if the citys pipe would maintain a constant pressure but it doesn't......the citys pressure varies ALOT. One second the main may have 100 psi 1/2 second later its 60 psi then maybe up to 80.....etc etc. This will cause all types of problems with over sized check valves and the pump itself.
Thats why you get the system engineered with the help of the system provider and you do not deviate. They know what works on their system now and what will work in the future as they design the sytem and more homes are connected. If you just go buy a pump that will work today with the system it may not work tomorrow when another house is added to the line and the pressure increases. You would simply have to replace the pump every time they added more people to the sewer. Thats why the city is specifying the pump and the size lines. If you follow their specifications and next year the pressures are too great for your pump to work.......THEY will have to get the system back to the specs and pressures it was designed for. So while you may get by with a cheaper pump today,next week you may be buying another one if you do not follow the specs.
To sum it up you simply do not size a forced sewer main like you do a water main. You do not worry about friction loss due to pipe size. You use the size line the city haprovided for the tap connection at the street. Over sizing WILL cause problems. The pipe will not clean itself and chat chat chat chattering swing checks that can damage the check valve and make the pump work harder.