I am in a similar position with limited time for Elite Dangerous PP, But I have managed to get the points above 1500 for the last few weeks with very little effort. I operate within a 50ly radius of a system on the border of my faction power, so it's a max of 3 jumps to reach the destination delivering propaganda. I then jump over to an opposing system to undermine, always very close as I am already in the 'contested zones between factions'. I undermine until I get too damaged to continue, tired, or a bad run of spawns...about an hour gametime maximum. I return to my 'home' to turn in the merits...usually between 15 and 300.
Collect 25 propaganda as I logout...and when I login I collect the next 25 and already have 50 to deliver as I rinse and repeat. It takes 2 to 3 game sessions to keep me in the level 4 PP. If I have a really good run of undermining I can get the necessary points in one session.
I have recently started to look at the PP tactics and start to take pride in my efforts as I see the opposition bars rising

. If I am not in the mood for PP I take outpost missions in the systems around me for the big payouts.