What's the normal water flow from a residential RO membrane?
Yes.  Depending on your membranes gpm rating the flow is relativly slow also the reject side will be faster depending on its rejection ratio.  Most are 8 to 1. Good nembranes will be high gpd with a 2 to 1 ratio   

Also these flow rates are if you dripped the product into a barrel. When you start adding back pressure. Like filling you tank. When it's half full you cut your production in half.  At 3/4 you cut another half.  Example.  50gpd becomes 25 at half full and 12.5 at 3/4.   Always go with the company with the biggest membranes and lowest rejection rates