In my mind, this is an additional 150+ SimObjects being loaded through Simconnect that, while I enjoy seeing them, are not necessary for me
The key sentence here is "in my mind".
GSX doesn't add 150+ Simobjects when it boards passengers, the thing that adds more objects ( in fact WAY more than 150 ) Simobjects is the AI Traffic program you are using, so it's there you need to work on first, and then, eventually, act on GSX.
You are probably thinking GSX has added "150+" objects, because you assumed that, just because your airplane has 150+ passengers, they'll be all be added together at the same time, which is not the case, since passengers are being removed as soon they enter the airplane so, even if you are boarding 150 passengers, you will never see them all at the same time.
What controls the number of objects, when passengers are concerned, is the Passenger Density slider, which controls how many passengers will be seen at THE SAME TIME, because those have an effect on the overall number of Simbojects visible in a scene at any given time ( currently officially documented as 1000 ). If you set the Passenger Density slider to a mid-range level, their number will be much lower and their contribution to reaching the maximum Simobjects limit will be very low, since you hardly see more than 10-12 passenger at the time so, clearly, it's no use to "sacrifice" GSX passengers that contribute like a 1-2% to the overall Simobject limit, if you don't work on the most impacting thing first, that is the AI traffic.
FS Traffic, at least, as an option to controls what it REALLY affect the overall objects number the most, which are Ground Services for AI airplanes. If you have like 100-150 airplanes, each one with multiple ground vehicles attached, you can easily reach the limit just with AI, even before GSX enters in the picture, considering even jetways DO count towards the limit and, big airports like KORD or KLAX or EGLL, come with a couple of hundred jetways on their own.
So, the two most impacting things that contribute to reaching the maximum number of objects are:
1) the number of AI airplanes
2) their attached Ground services objects, which are multiple objects for each parked airplane.
Reducing the 1st and disabling the 2nd item will result in the biggest contribution to keeping the overall number of objects under control.