Phone would randomly shut down to the point of becoming almost unusable. The charge would not hold for long.
Fifteen minutes? Yeah, maybe if you're used to having a soldering iron in your hands. For a mere mortal, allow much more time: for me, almost 2 hours.
But, got 'er done. So far, so good: charge is holding.
The instructions are generally solid and clear apart from the #3 ribbon attachment. It is not made clear that, unlike all the other attachments, this one does not completely unclip in a father/mother setup like the others. Instead, it is a ribbon which is held in a slot and clamped into place. I didn't get that and spent a long time trying to get it back into place. I had to resort to a YouTube search to figure it out.
If this process was made a lot clearer, it would have taken me far less time to complete. It's the only really fiddly part of the entire operation, and clearer pictures & instructions for this particular attachment would have simplified things.