Fifteen pounds.

That’s how much the job of a middle linebacker has been altered by since Kelvin Sheppard entered the NFL after being drafted by the Bills in 2011. And it’s how much weight he’s had to lose to keep up with the changing demands during a pro career that has brought him to the Giants.

“When I came into the league, it was: ‘We want you big, we want you in the middle, downhill, you’re a run-stuffing Mike [middle] linebacker,’ ” said Sheppard, who is listed at 249 pounds on the Giants’ website. “Now they still want you to do that, but a lot of teams, you have to be able to play on third down. You get to these spread offenses, it’s first and second down and they open the game with five and four wide receivers. So you do have to be able to run in space.”

That seems to be what the Giants like about Sheppard, a free agent whom they signed this offseason to compete for the starting job at middle linebacker. Jasper Brinkley took first-team reps throughout the spring and for most of the first two weeks of training camp, but Sheppard has been working with the starters on a more regular basis this week. There’s a good chance he’ll start against the Bills in Saturday’s preseason game in Buffalo, but even if he doesn’t, he’ll likely get plenty of snaps.

“He’s an instinctive guy,” Ben McAdoo said. “He gets football and has a nose for the ball. His energy impacts everybody out there. He’s a big energy guy.”

He’s still competing, though. The middle linebacker job remains wide open between Brinkley and Sheppard, and Keenan Robinson and rookie B.J. Goodson also have played the position this summer. Brinkley, in fact, was back with the starters for a few plays on Thursday and intercepted a pass.

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“It’s a great competition,” Sheppard said. “I believe if you look all over the league, it’s great competition. This is just a unique situation because there are guys being rolled in and out with the first group. But if you looked throughout the league, it’s competition in every training camp.”

Even before his recent opportunity as a starter with the base package, Sheppard has been playing a lot with the nickel group. That means more coverage, something he enjoys.

“I’ve been playing football since I was 5 years old, and the coverages are the coverages,” he said. “It’s not about your 40 time and things. That looks good at the combine, but I know guys that can run all day and you put them out there and tell them ‘cover-3’ and they hit their heads on the goal post. It’s about being able to be intellectual but at the same time have those tools and abilities to be able to keep up with guys that can run in this league.”

Brinkley was given the first chance at the job because he’s the only one who was here last season and has a knowledge of the playbook. He was the starting middle linebacker during the second half of the 2015 season and played well.

It didn’t take Sheppard long, though, to get caught up on the system. He’s done that before, having gone from Buffalo to Miami before signing with the Giants.

“I think it definitely helped me with the transition with it not being my first time having to go right in and learn a new scheme, and be expected to go out and perform right away,” he said.

McAdoo said there is no more learning curve for Sheppard.

“I don’t see him being behind anyone out there,” he said. “He’s a football get-it guy.”

Now he just has to go get the job.