The Seahawks have allowed only 15 punt-return yards this season, and none since Oct. 28. The secret to their success may surprise you. About a month or so ago, the members of the Seattle Seahawks’ punt coverage team began to realize that what is one of the oldest and most obscure of NFL records could soon be theirs. As the Seahawks prepare to play the New York Giants on Sunday, they have allowed just 15 yards on punt returns all season. The NFL record for fewest yards allowed on punt returns in a season is 22, set by the last of Vince Lombardi’s Green Bay Packers teams in 1967. That, though, came in a 14-game season. The record for a 16-game season is 49 by the Atlanta Falcons in 2008. Either mark is fine with the Seahawks. “If we can break a record, that’s definitely something we can take pride in,’’ said special-teams captain Heath Farwell. “That’s something we have been eyeballing for a while.” The last time the Seahawks allowed a punt-return yard was Oct. 28, when they held St. Louis’ Tavon Austin, one of the more dangerous returners in the NFL, to 7 yards on three returns. “That’s when we started talking about it a little bit,’’ said punter Jon Ryan. Two years ago, Seattle had one of its worst seasons covering punts, allowing 541 yards, third-most in team history. Ryan was the punter then, too, a year when he set a club record with an average of 46.6 yards. This year, he’s averaging 42.6 yards. But less has turned out to be more.