The White House has not held a press briefing in the last 15 days, according to records on the White House's website. The last one was held on September 24, 2012, by White House press secretary Jay Carney.
However, in that 15 day time period, and including today, there have been 11 press gaggles. Nine have been conducted by Carney, while 2 have been held by principal deputy press secretary Josh Earnest. Campaign surrogates David Axelrod and traveling press secretary Jen Psaki have participated in the gaggles.
But there's a big difference between a gaggle and a press briefing. Gaggles are limited only to those members of the press who are traveling with the president of the United States and are not video taped. Press briefings, on the other hand, are open to credentialed media (who obtain White House approval) and are on camera.
Gaggles tend to by shorter in length than a normal press briefing, usually being held for approximately 10-15 minutes at a time. And are these days very often held aboard Air Force One to accommodate the frequent campaign stops across the country by President Obama.