How to make smooth surface for OBJ files?

Hello,
I created a 3D Mesh model of a building using some images and the results look nice.
But if I look closer at the model surface, it's made out of much finer small surfaces.
If you see the images below, the left is the actual surface image (walls) and the right is my OBJ model.
And I think this is the main reason for having such a large file size and makes my project slow especially when I am trying to merge a couple of buildings in a single project.

Is there any way to smooth the surface so that number of faces can be minimized?
I just need to have a model that will look good enough, not in crazy detail.
But will this affect the original texture(image) allocated to each surface?

Thank you,

 

You can do that in 3D modelling software, like Blender.

One thing you can do is bake all of that surface detail into a normal map. It will look the same in Unity but, potentially, it could be much more performant.

Here is the most concise tutorial that I could find:

 

Thanks! I'll check it out.

 

What software did you used, to create it?

 

I used Context Capture from Bently

 

I see.

Blender could be in use indeed.
But if you maybe want some other tools to try, you may look into
Meshlab
and
CloudCompare

I used them in past, to clean complex multi-milion vertices meshed, before importing mesh to Unity.

 

If Blender won't choke on importing your unoptimized models, then its Decimate modifier will do the job.https://docs.blender.org/manual/en/latest/modeling/modifiers/generate/decimate.html