Easy switch between scenes here after allowing execution of the included script: 

• - When opening the blend file, there will be a popup window regarding the script, you need to click Allow
• 
  
• - To change for a different camera, you just choose between the scenes

If you have problem loading there a few tips you can try out 

SIMPLIFY:

Go to Render Properties tab (the camera icon Scroll down to Simplify)

- Enable it and set:

Max Subdivision: 1

Texture Size Limit: 1024

TEST: Render with CPU (For Testing)

Go to Edit > Preferences > System

Under Cycles Render Devices, choose CPU

Then render (F12)

If it works with CPU, the GPU is likely running out of memory.

USE SMALLER TILES

Go to Render Properties > Performance

Set Tiles to 256x256 (or even 128x128)

Smaller tiles use less memory per tile.