Unity 5 global illumination takes forever on simple scene

There's gotta be something I'm messing up but I can't figure out what it is. I have what I think of as a pretty simple scene:

1. 1 plane. Lightmap static. Standard Shader Opaque. 0 Metal / Smooth, Single color Albedo

2. 1 cube. Lightmap static. Standard Shader Opaque. 0 Metal / Smooth, Single color Albedo. Single color emission.

3. 1 tree (low poly model). Lightmap static. Standard Shader Opaque. 0 Metal / Smooth, Single color Albedo.

4. 1 Procedural skybox.

5. 1 Directional realtime light (the sun) with the standard settings.

My GI settings are pretty low:

And here's the end result of the scene:

My machine is a MacBook Pro, 16gb, 2.3GHz 4-core with a GeForce GT 750M with 2GB. I'm running Unity 5.1 and Yosemite. And it takes aprox. 14min to do the lighting for the above scene.

Either something is really wrong or I'm totally messing up some setting, cause it doesn't make sense that I would take this long. As a matter of fact, I think I was able to light map a more complex scene with even 8 for the realtime resolution setting about a month ago. Which makes me believe it's definitely got to be a setting thing. Thing is I can't remember if I changed something.

Any thoughts?