TECHNICAL REQUIREMENTS MODEL WORK WITH CGTRADER

You need to clean your mesh, removing polygons where they are not necessary.
I'm not an expert, but that's what I've been taught;)
An image might be more understandable :)
https://i.postimg.cc/NjP63Zmh/Sans-titre.png

Hoping it will help you.

Show us wireframe, it will be hard to tell it is posible or not.

if you use blender . so you can use un- subdivide .

i would say that you should bake texture maps for details and make big shapes with polygons