Unfortunately, as with a lot of film box office reporting, the claim does not account for inflation. The Times story mentions that another summer (2011) raked in $4.4 billion, but if you account for inflation then 2011 would pull ahead of 2015 ($4.4 billion is $4.67 billion in today's dollars). According to the The Hollywood Reporter, 2009 got $4.33 billion, which is $4.82 billion today. According to Deadline.com, 2007 saw at least $4 billion, which is $4.6 billion today, and 2004 saw $3.95 billion, which is $4.99 billion today.
A similar issue cropped up earlier this summer, with news stories touting Jurassic World as the no. 3 movie of all time domestically. But Box Office Mojo's inflation-adjusted list puts it at no. 23, below the original Jurassic Park at no. 16. An article in Forbes praises the hiring of Jurassic World director Colin Trevorrow to helm the ninth Star Wars movie while citing the claim that Jurassic World's opening weekend set a record, but when you factor in inflation, it's actually no. 2, behind The Avengers.
Ignoring inflation makes it difficult to accurately gauge how healthy the industry is compared to past years and to determine the summer box office's impact on Hollywood companies' bottom lines. The people making and exhibiting the films have to account for inflation when dealing with costs, so why ignore it when the money comes in? (While box office observers often acknowledge movies' costs, sometimes they ignore them when they might be useful. For instance, were the summer movies of 2015 also the second-most costly of all time?)
Some might call this nitpicking. So what if the summer of 2015 slides a few places down in the list? But when the front page of the daily newspaper in the city Hollywood calls home touts this summer as the second-biggest ever, it's bound to make a lot of people feel all warm and fuzzy when they shouldn't.