I have never had a puppy (not a big fan of that stage in a dog’s life), but I research dog behavior in all stages.
Puppies chew and nip everything, as it is how they learn about their world. It is completely normal. But it is important to direct the puppy to chewing appropriate items, and that doesn’t include any human body parts! At 15 weeks old, she should have already learned some bite inhibition from her siblings and mother, unless she was pulled away from them too soon. That is a chronic issue with many dogs these days.
You need to teach the puppy appropriate play behavior. It sounds like you are on the right track with what you are doing. To teach the puppy appropriate play behavior, hard biting should elicit a painful shriek or a loud noise from the human, like a rapt “eh eh”. Just like it does with the pup’s siblings or mom, this sends the message to the pup that this behavior is unacceptable. Stop interacting with the puppy. Get up, cross your arms, and walk away, ignoring the puppy for a few. Puppies and older dogs hate to be ignored. Sometimes the worse thing that you can do to a dog (in his mind) is to ignore him when he is just trying to get your attention or play. By walking away or even just crossing your arms and turning your back to him, you have removed the “rewards” (you and the playing), and you are teaching bite inhibition. Gradually decrease the pressure of the bite you permit and add a cue before yelping to teach a signal to the dog. Ignoring the dog is kind of like a time out for humans.
Another way is once there is biting, keep your hands very quiet and still and then redirect the puppy to other appropriate objects. Sometimes shrieking, then ignoring, and then handing the dog something appropriate to chew on is the way to go. Always have something available to transfer to her mouth. It may seem like you are rewarding, but if you do it correctly and with good timing, you are not rewarding.
Other biting, such as on pants leg or a shoelace, can be handled by distractions such as throwing a toy or a simple clap. Remember to NOT engage the dog verbally. Just talking to the dog by saying “no” reinforces the negative behavior. You just paid attention to the dog by opening your mouth to yell at it, so you are reinforcing the behavior. Reinforce only the positive behavior.
I know, it all seems to complicated, but it will work. I have seen it happen and I have trained it. Just take your time and be patient. Dogs are experts at reading our emotions and body language. Reinforcing unwanted behaviors is one of many mistakes we as humans make when raising dogs.