Visibiliy is the distance a which a black object of suitable dimensions, situated near the ground, can be seen and recognized when observed against a bright background;
It means the distance a which you can see a hard surface runway. With a 1500m vis you will never identify a grass runway.
What bright background? Snow? In 1500m vis, nothing will be bright since that depends on the reflectance/albedo of the surface and not much light is getting through anywhere if the vis is that bad.
It is all about contrast since that's what the human eye recognises (anyone who has flown on NVG will tell you that) - a grass strip in a field of light crops will stand out just as much as a tarmac runway. A grass strip on a grass field will be much harder to spot but not if it has distinct edge and threshold markings.