To answer Jeff's question, I am not noticing any abnormal heat on the phone.
I would never expect 0% to 50% in 15 minutes, unless there was a radioactive warning on my phone. This is the fastest charging phone I've ever had because of the turbo charger. Two hours and I'm full. I think if you are expecting 50% in 15 minutes, that would be like saying you will get 24 hours of "average" use in 15 minutes, because the phone is advertised as having 48 hours of "average" use. I have personally been averaging about 48 hours with 4 to 5 hours screen time on my phone with what I would consider light usage (mostly text, facebook, web browsing, email), so it is doable.
Going off of the advertised 48 hours:
100% = 48 hours of use
50% = 24 hours of use
25% = 12 hours of use
16.6%= 8 hours of use
So with the rate of charge of about 1% per minute that I have seen, it is logical for them to advertise 8 hours with 15 minutes of charge, especially assuming that you haven't ran the phone all the way to zero. Obviously some people use their phones harder that others, but I think most people could pull it off in a pinch if I had too.
Like I said before, your charging rate doesn't seem to be that far off the norm, but does seem a bit slower than expected. Maybe consider trying an outlet somewhere other than your home to rule out dirty power.
Edit: I just want to add that I have never officially timed the charging of my phone. All I know is that I have plugged it in, came back a couple hours later, and it was full. I have eyeballed it a couple times while charging just to see how fast it climbs, but never kept track of the charging.