The 17-year-old American improved her record in the 400 freestyle on Saturday by almost half a second. She collected her fifth gold medal of the meet in convincing fashion in cool but clear conditions on the last night of competition.
The world female swimmer of 2013 has had another exceptional year and wanted to finish her season in style.
"I knew it was my last race of the meet, and last race of the season," Ledecky said. "I've had a really good season. I wanted to finish on a good note. I didn't want to walk away from the meet with a 'That was OK' feeling. I dug in deep for the last 50. Put it all in there, the last 25."
It was the third time in 13 months she's set the mark in the 1,500, and the second in three months since her 15:34.23 at Shenandoah on June 19.
Ledecky holds world records in the 400, 800 and 1,500-meter freestyle events and is the world champion over all three distances.
New Zealander Lauren Boyle placed second in 15:55.69 and Brittany MacLean of Canada was third in 15:57.15.
Ledecky fell behind world-record splits before the halfway mark but was back in front of pace with two-thirds of the race to go and kept putting distance between herself and the old record in the last laps.
"Six seconds -- I was a little surprised," Ledecky said. "I figured pretty early on in the race that I was under world-record pace, I didn't know about the middle because I fell off a little bit.
"I was in a good rhythm (and) the momentum just carried me through."
Ledecky said the record was "tied" with her swim in the 400 as her favorite race.
"The 1,500 is not a huge priority of mine because it's not an Olympic event -- (but) it's certainly one of my favorite events," she said. "It was the last day of the meet -- last time I broke it, it was the first day of the meet -- so pretty different."
New World Record In Women's 400m Freestyle
Katie Ledecky set a new world record in women's 400m freestyle for her fourth gold medal at the Pan Pacific Championships.