No that’s completely insane and no one should be doing it.
If you’re in 5.5 you just have to wait for Epic to fix Lumen reflections with lightmapped GI.
Once it’s fixed, or if you are using an older version of Unreal where it still works (or deprecated reflections work), you should disable screen traces and use Lumen reflections with hit lighting.
Flat surfaces can use planar reflections, which is functionally similar to using a camera based mirror.
I would also avoid Nanite for archviz (or increase the fallback triangle percentage a bit)