Yes, setting the exposure compensation to -1.5EV works on these situations. But even after doing this, the image quality and focus accuracy of N9 is still not as good as N900. I think it should be caused by the CMOS size.

Damian Dinning had replied me several days ago on Twitter,
I asked why there is about 1.5EV difference in low light condition between N9 and N900.

And he answered it is due to the different light metering method between N9 and N900. There are cons and pros for both in different situations.