FrostyJas is right, Nanite can destroy precious performance by 3ms(on RTX hardware, at pretty low res too. )
I have an entire thread dedicated to teaching people about how bad nanite can be for many scenarios.
If you want to keep performance up, always check quad overdraw(control with polycount and LODs, keep the scene under a VERY lite sprinkle of green, no green is better) and shader cost(keep under the darker green).
Keep to that rule, and your game will be as optimized as 8thgen titles(many of them are more realistic them 9thgen ) and you will be 3ms ahead of the theoretical Nanite workflow.