I presume you use FSX which is 32bit - due to this OOM is frequent problem in the very-detailed sceneries / areas (P3D v4 is free from this problem).
FIrstly you can try to adjust your settings in accordance to the following guide: https://www.dropbox.com/s/w4wu3vqhf8jkm ... m.pdf?dl=0
Secondly please only try to install what is really needed regarding airports and their features. If you do not use any airport from the package, you can try to not install it. You can also remove "Airport Details" and "Static Aircraft" from it while still keeping the general layout.
Please also use the "Lite Texture Pack" when installing it (lower VAS usage).
Next option is to check a texture resolution - please check what is set in your sim and try with reduced parameter.
AI Traffic - please try to reduce it and if you have any other application responsible for AI traffic, please check the settings.
General recommendation is that "many airports" should not be active in the sim at the same time - it is best to activate those that will be needed for the flight, not 150 other scenarios at the same time. Flightsim loads not only those on which operations are carried out. Maybe it can also explain why OOM appears at the end of flight.