Building Lighting Takes Too Long

I’ve been following a Youtube tutorial series in order to learn UE4. I’ve run into problems however with building the lighting which gets to 2% very quickly then takes about 40mins to reach 4.5% while it “Processes Mappings”. It then very quickly goes from 4.5% to 100%.

This to me seems very slow and I suspect there’s a problem somewhere because the level is fairly small and the lighting quality is set to preview. Also there are only a point light, a spot light and the main light source (the Sun) in the level.

Things I’ve tried by reading other people’s answered questions:
-Adding a lightmass importance volume that encompasses the entire landscape.
-Setting EnableStandaloneMode to “True” in SwarmAgent.exe
-Viewing the level in “Lightmap Density” Mode to see the if there were any red areas

As a final note, when the lighting finally did build, the shadows which had previously been pitch black are now far too bright despite the “Environment Color” in the World Settings being set to black. Not sure if this is a separate issue but I thought I’d write it in case it’s relevant.

PC Specs:
-Windows 7
-16GB RAM
-i5-3570K CPU @ 3.40GHz
-GTX660-Ti