I think this is hindsight bias. You know that the accident happened, you know the time claimed (15 seconds) and therefore, 30 seconds is a better number. If the post had said the unfortunate had waited 30 seconds, would the correct time to wait be 1 min? And if one minute was claimed, would the correct number be 3 minutes? I doubt the shooter waited exactly 15 seconds, I don't keep a timer on the bench, I doubt the shooter does either, could have been more or less.
The fact of the matter is, old ammunition has problems, and thinking that there is some number, or a rabbit's foot somewhere that will prevent an accident, is wishful thinking. Instead of a hangfire, that shooter could have had a squib, next round down the barrel could have blown the barrel and action. The fact that the original owner of that ammunition, the Pakistani military, decided that ammunition was too dangerous to store, or issue, to its own troops, ought to be pointed out to potential buyers of surplus ammunition. But, it is not. I have never read anything in the popular in print press educating the shooting public about what "not to buy".