View Layers Ram memory cost Question

Hi there!,
trying to understand how to render in separate view layers for compositing…

I have a big scene with collections, its ok until i create a new view layer, I thought that geometry would be linked or instanced but ram memory doubles every time I create a view layer…

If I create a blank view layer (with all collections turned off) its all ok, no memory cost, but as I go turned on the needed collection is like reloading the geometry (and ram memory rises as if I bring new geometry to the scene)

For example, I have a block of geometry that I want to create a separate AO pass (with custom shader etc…, not the pass built in), then I need the same collections to work on both view layers (name it “render” and “AO”, and an override shader for the second one)

So with the “render” layer view ram memory is at 20%, and when create the “AO” view layer, ram increases to 40%

Is this the way to go or is there something I don’t understand?
Many Thanks guys!!

edit: Blender 3.0 on linux (Pop Os 21.10) if this info helps…

edit2: I think I found something related to the modifiers (subdiv, etc…), I convert all to mesh and the RAM impact has lowered 50%…so…for render / view layers… better without modifiers…can someone confirm that? Thanks!!