Exceptionally bad performance

Let me first start with my system specs:
CPU: Intel i9 13900k
Motherboard: Gigabyte Aorus Master
Memory: 32gb 6400Mhz G.skill DDR5 (X.M.P profile enabled).
GPU: RTX 3090 (full cover water block).
HDD: Multiple Samsung SSD m.2 drives 960 pro, 970 evo etc
OS: Windows 11 Pro
Cooling: full hardline Liquid cooling loop, GPU EKWB full cover water block
PSU: 1200w Gigabyte

Why when I start a brand new blank scene, I use the Env light mixer to put a sky light, directional light, sky atmosphere, exponential heigh fog and volumetric cloud. I then put a post processing volume, set to unbound. put a basic landscape, just flat with some painted hills etc. I then put a rock or two (and I mean a rock or two at a push) from megascans, and perhaps maybe 1 tree and suddenly my frame rate drops from 120fps to 60 fps…exactly half my frame rate for 2 objects in my scene maybe 3 if we are being very brave that day. Heaven forbid I paint some foliage because then the frame rate drops into the 15fps - 30fps range. Enabling or disabling nanite makes no difference to my fps.

I have brushify enabled for the painting of textures on my tiny little minute landscape. with my rock and tree. The tree comes from Epics tree library, you know the megascans ones that are supposed to be good for making entire forests and biomes.

This is killing my workflow. I enable lumen or disable it, no difference, delete post processing volume makes zero difference. enabled or disabled hardware raytracing no difference. frame rate is shocking. I have no idea what I am doing wrong but this really can’t be right on a system with these specs?

In game try pressing F5 to see if you have any overly complex materials. Anything on the far range of the spectrum (light red => white) could be tanking your performance.

With foliage that is translucent textures instead of masked can cause a massive overdraw penalty.