Have you tried to finetune it?View > Rendering Options > Rembrandt Options. Try to lower the number of cascades, texture size, disable ambient occlusion etc.
For me it depends on the aircraft : All ok with the Seneca Ok with the Lionceau APM20 but the propeller is always visible Not ok with the Cap 10B, too slow Not ok with the Cap 10C, idem Not ok with the Beechcraft, idem
I don't know what are the aircrafts running with rembrandt. If someone indicates me, I'll test them.
Have you tried turning down all of the rendering options? I find that if I don't, the Beechcraft and the C172P perform badly from outside views. (it seems related to the propellers or spinners on the Beechcraft, the livery on the C172P, but I don't know anything about optimizing 3D models...)
So, if I set the Antialiasing to 4 - instead 8, all is better. And I don't turn down the rembrandt rendering options. But for the C172P and the Cap 10B (I didn't try the others) the livery disappears. Just the Seneca maintains his livery (for this plane there is no choice of livery).
I'm not sure why we even permit anti-aliasing options of 4 or 8, it's just giving people ways to make problems for themselves. Personally I can't see any great difference beyond 2x, but I'm sure other folks will disagree