It’s set to a 30%/70% mirror and glossy mix.
The mirror material type is one of the slowest to converge in LuxRender. I stopped In the Elevator at 7500S/p, and it still has an incredible amount of noise in the mirror surfaces (at least when viewed at full resolution, not downscaled for dAs preview window). The other renders I’ve done that include mirror surfaces have also suffered similarly.
The most recent weekly 1.3dev build also includes LordCRC’s changes to the glossy material to allow for higher, near-mirror roughness values. (It previously clamped roughness away from this due to numerical stability issues.) So I don’t know if those changes would allow you to get the effect you are looking for without mixing in the mirror surface.
Highly glossy and/or specular materials in general, however, take longer for Lux to converge. You said you’re currently just shy of 1300S/p. I generally consider 2000S/p the minimum for any render I do, and when there are things like a lot of volumetrics or other slow-to-converge surface types, will take things much further. I ran King to A5 to 15,500S/p, for example, because of all the glass2 volumes for the chess pieces.