Yeah, I’d definitely not use Material Preview for this!
The performance might also (partly) be a Blender Version issue; in 4.2, for instance, EEVEE is ‘new-born’ and Material Preview uses EEVEE…
And Simplify has different Settings for Viewport and Render; Render affects only actual Renders! Everything else (including Material Preview and Render Preview) falls under Viewport.
But also, if only the scrunchy has Subdiv Level 4 and the rest is not higher than Level 2, setting Simplify to a Max Level of 2 won’t have much effect.
