Google Sketchup 2015 and Google Sketchup 15.3.331 still free for commercial use.?

I believe you have to go back to a Google version of SketchUp like 8. Google sold SketchUp more than four years ago, though. There is no “Google SketchUp 2015” as you’ve written in your title.

The Google versions of SketchUp have not been supported for years. Some of the features no longer work, either.

Just buy the license for the current version and be done with it.