YES…6 materials per book mesh is a lot…I would suspect you’ll get quite a bit better performance if you reduce that to even 2 much less 1…
Make sure you’re using a Material Instance as well for the books…I imagine you are but thought I’d mention it…
Also when I build lighting it helps a ton with my FPS…Go to your “world settings” and then “lightmass” and set Static Lighting Level Scale to 5 (heck even 10)…as long as you’ve set your Lightmass Importance Volume you’re build time will reduce drastically and you’ll be able to see if your performance reduces after building lighting…Change it back to 1 (or smaller) when you are building for real/show though…
Last idea/resort - Create the library like destructible meshes are made …build a book shelf and it’s books as 1 mesh…then replace it with the movable books version (and all of the different book meshes in the same place as the Whole version) as you interact with it…I don’t know the nature of your project though so this may not work if you’re going to slowly move all the books around or something cause by the end it’d be back to the way you have it now with a ton of meshes everywhere…
anyways nice start to a scene…hope it all works out…