Most models in sketchup are insanely inefficient in game engines. To help some of the problems you need to combine the meshes into larger chunks.

as an example, a door handle made for games might be 2 pieces(the moving part and the part bolted to the door).

Sketchup might make it into 60 or 600 different objects(the key hole, half the door knob, the other half, 1/16 of a part of the lock handle, you get my point).

A ton of different objects cause alot of unnecessary draw calls(which slow down frame rates).

You want to combine the individual parts of a skethup mesh in blender and the biggest hurdle is the need to name each UV Map something unified. aka all uvmaps need the same name.

To do properly combine

• open up the python editor(click the circle with an i in it) top left corner, stretch the window out

see this gif if you cant find the python editor https://i.gyazo.com/889ae5b958904f88475e9f177f56d10c.gif

• Select all objects in the scene (hit A until everything has orange outlines around it, OR manually select parts you want to combine)

Paste this into the python editor

import bpy

for obj in bpy.context.selected_objects :
for uvmap in  obj.data.uv_layers :
uvmap.name = 'UVMap'

Tab spacing is important on this, and reddit deformats python. see this pic for correct tab spacing. https://i.gyazo.com/a1a2e0818facb11f9a20856bf3a0613f.png

• Check to see that everything has the same UV map name. YOU WILL LOSE ALL BUT 1 UVMAP IF YOU DONT DO THIS.

see this image for where to check (right side properties box in the sub menu that look like a triangle) the UV maps should all be named UVMap https://i.gyazo.com/e13324740acae87a96b464c4e80b234c.png

• Then hit ctrl J to combine everything you want combined

• then export with these options checked https://gyazo.com/52b59acccba27b6ffc76c51187d3b32a