Especially when departing busy airports we recommend a couple of tweaks
The first tweak is to set your AI traffic to "use generic plane models" - if not, you may run the risk of having multiple different plane types spawning at the same time, which can be a drain on your resources.
You can also specifically disable any addon aircraft from spawning as AI in the aircraft.cfg file by changing the parameter isAirTraffic to 0
The Fenix should have this set by default.
Furthermore, Photogrammetry is known to reduce performance and give poor visuals. We'd recommend turning this feature OFF in the MSFS General Options > Data.