That's good in concept, but will it actually be enforced, or will we then ignore 15 seconds? I actually think 6 seconds (which is supposed to start once the GK has had time to gather himself from the ground and stand up) is plenty of time. (If 5 seconds is enough for a basketball player to throw a ball in against a pressing defense in a compact space, and 6 seconds is enough for a restart in futsal, then 6 seconds is plenty of time for a GK who always has the option of just punting the ball upfield.)
We don't fail to enforce it because it isn't a long enough time; we don't enforce it because the sanction is so harsh and no one else enforces it--so we're likely going to end up giving at least one caution if we do call it. I wouldn't mind seeing a trial of strict-ish enforcement (perhaps warning at 5 seconds and called at 8) and see what happens. I think calls would be rare. And we could take pressure off the call by softening the sanction to a CK or something similar rather than the IFK in the PA.