Yes, your 150-500 would become a 450-1350 (and still a F5-6.3 because it is an adaptor, not a converter so you aren't losing any "stops"). In the UK the V1 is becoming cheap compared to what it used to cost but then it was seriously overpriced.
I do not own it but I did consider getting it. It is light, has a good autofocus, can get many frames per second, has video and its sensor is great with its magnification. The image quality could be better, especially at high iso but you can find online some very nice photos taken with that camera. Another minor downside is I believe you only get a single autofocus, not a continuous one.
To be on the safe side, try the V1 with your lens because it looks there are some troubles with the V1 not recognizing some Sigma lenses.
http://forums.dpreview.com/forums/thread/3120336