Bidirectional SurfaceIntegrator does not work properly in LuxRender, it has problem with surfaces with high reflectivity. Use path integrator instead, the image will not be so nice, but at least you will be able to have an useful image after some time.

Decreasing the specularity of the materials can help, but then you will lose all the benefits and beauty of bidirectional surface integrator

Stupidity also evolves!