@Nicolas3D : What I have observed is, if we are using other lights along with Skylight we don’t need the high Photon Density(Direct as well as Indirect). Increasing the Photon Density, increases the build time by the factor of amount of increase from default value(400).
@ : Please correct me if I am wrong.
In your scene, you can get the same quality with the following settings with reduction of build time by around 60%:
Use default BaseLightMass.ini with only NumHemisphereSamplesScale > 64
Static Lighting Level Scale: 1
Num Indirect Lighting Bounces: 100
Indirect Lighting Quality: 10
Indirect Lighting Smoothness: 1
You can play with Indirect Light Intensity of SkyLight and Directional Light to get this quality with much faster Build time.
@: It took around 40 mins for light build. Also I have observed that these values differ substantially depending on scene. If scene has lot of closed space, as in case of Interiors, it is very difficult to get good lighting with only Skylight even with lot of changes in BaseLightMass.ini.