Adding the fire extinguisher to your scene is easy done by simply appending the fire extinguisher group to your new blend file. Remember to copy the texture folder as well.  

Decreasing render times

That little piece of glass in front of the gauge will increase render times quite a lot. So, if you don't really need it, you could simply move the glass faces down into the extinguisher, hiding them. -10cm on Z axis (-0.1 blender units) will do the trick and you can render with a lot less samples and a lot quicker. That way the glass is easy to add back in place in case you need it later.  

Differences between blend files

The Cycles and LuxRender high poly blend files differ in material setups and also the little piece of glass in front of the gauge has two surfaces in the LuxRender version because it require glass to have thickness. Other than that they are the same. The low poly versions differ in material setups as well. Instead of using the three textures (diffuse, bump and roughness) that the high poly versions uses, the low poly versions uses only a diffuse texture. Both the Cycles and LuxRender low poly blend files are not using the glass in front of the gauge.