"I really didn't want to go out too hard because I feel I am better if I have a more controlled first half and a strong back end. I was really happy with how it went."
Out in front, Katie Ledecky (United States) and 2011 world champion Lotte Friis (Denmark) pushed each other to a thrilling world record for the 16-year-old American, while Boyle edged clear of Spaniard Mireia Belonte Garcia and closed the margin on the leaders over the final 400m
"I knew that Belmonte in lane six is such a good racer and I was scared that she was going to roll me. But I managed to stay ahead and finally break her.
"I just can't believe I've got a medal in the 1500. It's amazing because it's the first time I have swum this race in a proper championship. It is really surprising and I am so happy."
Boyle now has two full days rest before preparing for the 800m freestyle, where a medal would give her three for the championship, to equal the performance of Danyon Loader who won a silver medal and two bronze at Rome in 1994.
Tomorrow night will see fellow Kiwi Glenn Snyders in the final of the 50m breaststroke after he pushed to third in his semifinal and sixth fastest overall in 27.22.
Snyders, now based in California, clocked a year's best 27.27s to be third fastest in the heats behind top qualifier Cameron van der Burgh (South Africa), the London Olympic 100m breaststroke gold medallist.
Snyders drew beside the 2009 50m world champion in the semifinal, improving on his morning swim.
"I am happy. It is my first individual world champs final so that's great, and I went faster than in the heat," Snyders said.
"I missed out on the 100 which was disappointing. Today was another day and had to prepare and focus."
Wellington's Gareth Kean finished eighth in the final of the 100m backstroke, not able to finish off after a strong first 50m, clocking 54.25s in the final won by American Matt Grevers in 52.93.
"It was an all or nothing approach, just trying to get out there and hold it. That last 50 was pretty hard. Obviously I didn't get the result but I had a go and just see," Kean said.
"The key things like the start and turn felt good. Now I have a day's rest and see how I can go into that 200 back and get fresh again and give it my all."
Earlier, Wellington swimmer Samantha Lucie-Smith, in her first world championships, finished eighth in her semifinal of the 200m freestyle, after taking nearly a second off her previous best in qualifying.
