Many new divers try to stop their ascent at 15 or 20 feet and begin their safety stop. I learned a long time ago (after being a guide for hundreds of trips) that this is NOT a good stategy.
When I was a guide, I used to "make" all the divers, to STOP the ascent at 30 FEET! If they accomplish this, get neutral and calm, then the very gradual ascent upward to 15 feet usually goes well. If they totally scew up and miss the 30 foot stop, they will usually get it sorted out by 10-15 feet and can still pull off a decent stop, because their goal was a stop at 30 feet.
If the new diver tries for 15 ft and overshoots only a few feet, the bouyancy change is too rapid and they almost invariably pop to the surface.
The stop at 30 feet only needs to be for 30 seconds or something. I used to make up some BS, like, "on this boat, we are all going to stop at 30 feet and check eachother's air pressure".
Using a safety sausage with some line and a weight to help you hang at 15 ft will make things much easier. (Just remember to STOP AT 30 FEET, get the sausage out and ready to deploy) and then come up a little and deploy the marker.