Is that 19m 36s for the first render? If so that’s terribly slow, and probably something wrong with your scene setup. I can have a look at the scene file if you don’t mind?
I’d recommend not using the material database, and instead actually setting up your materials yourself. That way you know what settings each material has, can control the diffuse/glossy settings properly (try keep all diffuse colours < 0.8) and also the render engine settings (Bi-Dir, etc…)
The small S/s and really high Eff generally mean that your light sources are somewhere particular hard to locate, and MLT is doing the best it can to render them.
Ok, I had a fair bit of trouble getting the scene to render, what version of Blender and LuxRender are you using?
I would suggest using Blender 2.72 and LuxRender 1.4RC1.
I re-did your materials from scratch, I would suggest you do the same, at least for these materials:
The Wood/Floor, just a simple glossy material with a uv-wrapped wooden floorboard texture will render far faster than the procedural material you have.
Again a simple glossy material (high roughness) will do for the wall paint
Use the LuxRender [Blender] lamps instead of meshlights; The point light in Blender can be used as a physical size lamp in LuxRender, but renders faster as its not a mesh.
Here’s a render using the Bi-Dir integrator, and the Sobol Sampler, ran for 2 mins on a i5 4440