As we're all comfortable with numbers plucked out of the ether, let's use yours:
1. The group of low-wage workers produce on average $9/hr.
2. A minimum wage of $15/hr is introduced.
3. The income of 10% of the group falls to $0/hr because they lose their jobs, a fall of $9/hr * 0.1 = $0.9/hr on average.
4. The income of 90% of the group rises to the new minimum wage of $15/hr, an increase of $(15 - 9 = 6)/hr * 0.9 = $5.4/hr on average.
5. The net change in income is $(5.4 - 0.9 = 4.5)/hr on average.
So with all these contrived numbers the introduction of the minimum wage raised low-wage worker pay by $4.5/hr on average. Is that bad for low-wage workers?
Of course, really, we should just take ryandamm's advice here [0] and stop trying to provide our arguments with the air of rigour by throwing some made up numbers around.
[0] https://news.ycombinator.com/item?id=14381189