Staff members found the dogs caged in three small wire crates, left in front of the humane society's administration building Friday.
According to Ricky Whitman of the Pasadena Humane Society, no one has ever abandoned that many dogs at their shelter.
"Usually if someone is going to abandon an animal, it will do it one animal," Whitman said. "To have 15 is a lot of animals at any time."
Abandoning a dog is a misdemeanor that can lead to a fine and as much as one year in jail. But police have a few clues as to who the offender might be.
A blanket in one of the cages was monogrammed with the name Mike. Surveillance video also captured a white truck carrying a visible cage pulling up to the building 5:30 a.m. Friday.
Whitman believes the incident is a shame since the humane society offers many support services that could have helped the owner.
"We offer Chihuahuas spay and neuter for free at no charge if you live in our service area," Whitman said. "We have food banks for animals if you're having difficulty feeding your animal."
Hollywood helped popularize the breed by releasing the movie "Beverly Hills Chihuahua" in 2008. But Whitman says the recession hit hard. Within the last few years, 30 to 45 percent of the sheltered dogs at the Pasadena Humane Society have been Chihuahuas.
Some of the females dumped Friday appear to have been bred.
"All of the animals have not been spayed or neutered so we can assume that it's probably from a backyard breeder," Whitman said.
Anyone with information regarding the culprit is urged to contact the Pasadena Humane Society at (626) 792-7151 ext. 102.
In the meantime, the public is urged to provide these dogs with new homes. The humane society says once the dogs are given clean bills of health, they will be ready for adoption.
For more information, visit the Pasadena Humane Society website.