If you read one of the reviews on the board at that site:
I just received an 8 channel and a 2 channel relay module today. It took me a while to figure out that the pins have to be driven low, not high, to cause the relay to activate. Not only that, but the current sink is less than 3 mA. I don't know what the "15-20mA Driver Current" is all about.
Maybe that current is the amount of current required to switch the relay because it does seem high for an optoisolator. I think you are good to go with this board.