I've been pondering the same thing. The question you have to ask yourself is what do you think the average rate of difficulty increase you expect to see? To me it seems that we are entering explosive difficulty growth. The next difficulty increase to hit looks to be about 30%. If that is sustained you are looking at 50-60% growth per month. While not perfect I found a good calculator I like to use. It would be nice if it did more than monthly difficulty increases but it's close enough for rough numbers.

You can find it here: btcinvest calculator

I plugged some numbers in and assuming 50% difficulty growth per month you would get about a 66% return on your .15 btc invested over one year. ROI would be achieved after nine weeks of hashing assuming it starts on November 1. So you are looking at ROI, with these assumptions, by January 1.

You can find the calculator with the parameters I used here: btcinvest assumptions.

The two major factors here are of course delivery time and difficulty.

I'm very tempted to jump in on this. I'll probably make a decision early next week but wouldn't be able to get funds for many days.