Just completed the install. Used the 18# hammer spring.
First of all the firing pin roll pin mushroomed a tad with a legitimate 3 mm roll pin punch. Not enough to mess with the function of it, but it mashed up the end that can be seen by the naked eye, and for me I don't care for that. So the stocker went back in.
So hammer spring, plunger spring, and sanded the firing pin block. No noticeable difference in double action. Less gritty, that is about it. Single action is butter and light, but it has been since I had about 1000 rounds through it.
Now take that with a grain of salt. The hammer spring plastic plug is a (foul language removed) to get back in without the lanyard loop on the end, so I can barely feel my finger tips in the mean time.
A lot of people say they have had no issues stepping down to the 15# hammer spring, but this is my night stand gun so I'm a bit nervous. As of right now I want to, because I can't say that I feel as if I gained anything. I'm going to hit the range and make sure the gun functions and see if there is any difference.