I think 15% was based on a 10ml sample.
If you were to do a 5ml, perhaps adjust to fit? 7-8%
I don't know what would happen if you exceeded, or reduced the alcohol. There is a sure way to know, try it
I would do it, though, I believe this process is to aid with steeping, rather, prevent the need to steep. I don't steep anyways, so, I don't know if this process is beneficial for me. I might try it someday soon, just to say that I have.