In discussions I have had with my uro, his "training" injection is (using a BD 1ml syringe) is .1. After that, he says go up to .11, then .12, stepping until the desired balance is achived, but no more than .2. His thought is that going from .1 to .15 is too big a dosage increase.
Remember that it may only be .1 and .15, but .15 is 50% more.
As explained to me, the impact is not "linear", and making large quantity steps up is not wise unless you are near an emergency room you trust - sounds a bit like a joke, but probably most serious.