Are you using Global settings in Graphics? If not, I suggest doing so, and start with Low.
Use a Low-impact cockpit (C152 - analog gauges only) and a Glass Cockpit (suggest C172 G1000) as your baseline planes for testing. Airliners have serious FPS impacts all on their own.
Traffic is one of your biggest ROI. Use Offline AI, reduce the count down to 10 each for GA and Airliner. For ground, leisure and commercial marine, try 5.
Turn down your static planes, personnel and vehicles at the airports - to 5.
Those are the biggest CPU cycle consumers outside of the cockpit, with the exception of a High or Ultra refresh rate on Glass Cockpit.