(CNN)In the absence of dancing bodies and screaming fans, the theater inside Planet Hollywood Casino and Resort is shiver-inducingly cold and cavernous. The sniffles emitting from A.J. McLean and Kevin Richardson echo a bit as a result.
Backstreet Boys share their secret to longevity
They're fighting sinus infections. In fact, all of the Backstreet Boys are, Richardson said.
"I just had sinus surgery," McLean shared. "Now that I can breathe, it's awesome. But now I'm getting everything."
The nearly 5,000 fans that were in attendance a little less than 18 hours prior certainly didn't seem to notice.
The energy was, you could say, larger than life on opening night of the Backstreet Boys's residency at The Axis, a space that also hosts Britney Spears's Pieces of Me show and Jennifer Lopez's All I Have. (Lopez's show vacated days before BSB's March 2 opening, leaving them with just a couple of days to practice on their new stage.)
Organizers call it one of the fastest-selling shows in Las Vegas history. It also happens to be one of the biggest milestones in Backstreet Boys history.
The idea to do a Las Vegas residency was first floated around 2013, said Richardson. The Backstreet Boys were on their "In a World Like This" tour and Spears had just launched her show to much excitement.
"One of us or one of our managers mentioned, 'Hey, that'd be a nice place for you all to end up some day,'" Richardson remembered.
The dream became a reality after their last tour, when Live Nation made the band an offer.
"It's definitely a process to get to this point," McLean said. "But we finally made it. Here we are."
The show has come together in a mere eight weeks.
The band aimed to create a show that simultaneously highlighted their strength as a vocal group and honored their past with choreography throwbacks. (They did away with the "typical boy band [with] headsets thing," as McLean put it.)
They enlisted the help of four choreographers, including bandmate Nick Carter's former "Dancing with the Stars" partner Sharna Burgess. She helped them craft a ballroom-style dance that is featured during their performance of "Undone."
"Getting ready for something like this, there's lots and lots of ibuprofen involved," McLean, 39, joked.
"I'm not a spring chicken anymore," Richardson added. "Physically, we had to take care of ourselves."
The Backstreet Boys, indeed, stopped being boys quite some time ago. They're all married and fathers.
Carter, the band's youngest, joined the band when he was 13. He is now 37. Richardson, the oldest, is 45. (Howie Dorough, 43, and Brian Littrell, 42, round out the band.)
McLean said they're lucky to have had some fans who have stood by their side through their entire journey so far, dating back to the days before they were signed by a record label and touring high schools in attempt to get exposure.
The Larger Than Life show is an attempt to bridge the gap between their fans who stayed with them and the ones who haven't seen them in 10 years, Richardson said.
The set list reflects that.
"I Want It That Way," "Shape of My Heart," "Everybody (Backstreet's Back)" and other radio hits are well represented.
Then there's songs like "Darlin'," which was never released as a single but tends to be a favorite of the hardcore fans, Richardson said.
"Had we gone with the original amount of songs, it probably would have been a three or four hour show," McLean said. "Our die-hards would have been like, 'Yes! Four hours? Fine! Keep on going!' But we'd be dead."
"Til death do us part" is in some ways a Backstreet Boys motto, of course.
With 24 years under their belts, they've survived longer than similar bands that emerged in the '90s. They've gone through lineup changes (Richardson took a break from the group from 2006-12). They've battled record companies and former managers. They even released a tell-all documentary in 2015 that revealed Littrell's ongoing struggle with a condition called vocal tension dysphonia. (Richardson says his cousin is still "working through it" and "some days it's better than others.")
The Backstreet Boys have it all on the table.
"Sometimes we laugh like brothers, we fight like brothers. We're a family," McLean said, adding that they recently started group therapy. "This is a marriage."
McLean thinks age has helped them find "a newfound respect for each other."
"Nick is the most recent to join the daddy crew. So he, I think, sees things a little differently now," McLean said. "I think we all relate to each other better now than we ever have."