Answer based on context:

The Lions needed all 60 minutes to overcome four turnovers and a minus-6 differential in penalties to overtake the Dallas Cowboys. The game started slowly, with just three scores in the first half. Detroit struck first with a 90-yard drive, highlighted by an 87-yard pass from Matthew Stafford to Calvin Johnson and capped when the two connected again on a fourth-down 2-yard TD pass. Dallas got a second quarter field goal of 53 yards by Dan Bailey to make the score 7-3. On the Lions next possession, Sean Lee intercepted Stafford for the second time in the game and returned the ball 74 yards to the Lions 4 yard line. Two plays later, Tony Romo hit Dez Bryant with a 5-yard TD pass, giving Dallas a 10-7 halftime lead. Bailey converted on another 53-yard field goal in the third quarter, putting the Cowboys up 13-7. David Akers narrowed the lead to 13-10 with a 20-yard field goal early in the fourth quarter. But Dallas struck on their next possession when Tony Romo connected with Terrance Williams on a 60-yard TD pass play, putting them up by 10. Detroit's Joique Bell capped an 80-yard drive with a 1-yard TD run to cut the lead to 3 again, at 20-17. Dallas again went up 10, as Romo and Bryant hooked up for their second TD pass play of the day, this one going 50 yards. The Lions came back with a 1-yard TD run by Reggie Bush, on a drive that featured a key 54-yard pass from Stafford to Calvin Johnson, cutting the lead to 27-24. The Lions lost the ball on downs with 1:24 left in the game, but Dallas could only take 22 seconds off the clock before Dan Bailey put them up 30-24 with a 44-yard field goal. The Lions began an improbable 80-yard TD drive with just 1:02 remaining on the clock and no time-outs left. Stafford hit Kris Durham with a key 40-yard pass that put the ball at the Cowboys' 23. Stafford then hit Calvin Johnson with a 22-yard pass on the next play that got the ball to the Dallas 1, but the clock was still running. Instead of spiking the ball to stop the clock after the Lions quickly lined up, Matthew Stafford lunged over a pile of linemen and stretched the ball over the goal line for the tying touchdown, with David Akers' extra point giving the Lions a 31-30 victory. The Lions tallied 623 yards of total offense on the afternoon. Stafford was 33-of-48 for 488 yards and one touchdown.  Most of his passing yards were to Calvin Johnson, as the Lions wideout caught 14 balls for 329 yards and one touchdown. Johnson set an NFL record for receiving yards in a regulation game, and was just 7 yards short of the full game record of 336 yards set by Flipper Anderson in a 1989 overtime game. Calvin also tied Lance Alworth's all-time NFL mark with his fifth career game of 200 or more receiving yards. The Lions also became just the second team in the last 56 such games to win despite a minus-4 turnover differential. The only other team to accomplish this was the New England Patriots in a 2007 game against the Miami Dolphins.

How many incomplete passes did Stafford throw?
15