I've done the "15 min" job on most of my AR's, and they are reliable, with pull weights at about 4#, crisp with very little over travel.
I'd recommend anyone thinking about doing it to have a complete set of spares in case you go to far, but if you study how the parts work together, and take your time, you should be able to get good results.
One thing I do is cut the hammer hook off, so the hammer looks like the "competition" hammers JP sells for $50 :/ And, I do not use the notched hammers.
This seems to make a difference in the reliablility, I use CCI SRM primers as a rule, and I do not have any misfires, ever. Speeds up the lock time, too.
ETA I realize the term "hook" might be confusing, I don't mean the sear hook. Modified hammer below:
