Basically your RO is removing just under 97% of the dissolved solids. So that's not too bad at all. I am guessing it's a fairly small RO?Tap is 310 ppm ish and the RO is currently 9.8ppm. Is that ok?
With a booster you might get a slightly better % removed but only 1 maybe even 1.5% but you could probably reduce your waste % a bit to 60 waste to 40 pure or 55 waste to 45 pure as long as you flush the membrane regularly.