I am going to get myself in trouble, but....
I think that at 15 grains in an old revolver, you would not see much difference.
I get myself in trouble here because I am not a purist and in a world of purists, a guy who shoots as I do appears not to care about performance.
I call upon the more exacting shooters in the group to endorse or dispute my opinion.
I just think you would not see that much difference unless you are using a chrony and a bench rest. If you shoot Hornady round balls you will find enough difference in the diameters of various balls from the same box that you would wonder if that is impacting accuracy. It probably isn't but you would wonder. (I do)
#10 Caps should work and as long as the nipple is clear you should get good results.
Goex or Triple Seven is easy to find in most venues and #10 caps are fairly standard.
My reading of history convinces me that most bad government results from too much government. Thomas Jefferson