Light mapping got stuck on "7/11 Light Transport" and then failed

My scene had a real estate architecture and some terrains in it (screenshot is attached). When I started baking the scene only with directional light it took too long at "7/11 Light Transport", I left the computer on for almost 11-12 hours but still it wasn't completed when I checked it after that and finally I had to stop the process and close unity. I read all the forums on it and tried to apply whatever is suggested over there but the issue was not resolved. PLEASE HELP
Thanks in advance

 

What I did is I deleted the terrain I was using and placed a quad with the same texture and placed some trees manually, now Baking took less time as compared to before but still too slow, I had to cancel it again when it was at "6/11 Visibility". these are the Lighting settings which I was using, hope they are ok

 

Hey, Thanks for the solution which you gave last time, I used Real time GI with resolution of 0.1 and it really started baking faster as compared to the Baked GI, but again I struck with a problem It was baking faster but now I started getting "FATAL ERROR:could not allocate memory system out of memory" and unity started crashing, here's a snapshot of the error. I read other forums regarding this issue some of them asked to compress the size of the texture, but even after compressing each texture from 2048 to 512 I was getting this error

 

SpiriTx, I reduced the resolution to 0.001 but unfortunately no use, my light mapping got struck thrice at the same point ""Light Transport 130 jobs". Is there any problem with lightmapping in unity 5, because I've used 4.6 version of it, there Baking didn't showed any of these kind of issue. OK I thought of baking one object at time but again unity 5 doesn't have "Bake Selected" option. What if my scene is huge?? Doesn't matter even if its taking time it should be baked at last, but unfortunately unity is crashing all the time, I read so many forums on it, and tried everything what they said still I'm getting problem And I don't think so my scene is as big as any other game, here joining a screenshot of my scene.