Prosecutors said they would ask the parole board to force him to serve the entire sentence.
"We are hoping that period of time might change his behavior, but you never know," prosecutor Maurice Arrisgado said.
Public defender Teri Marshall said Royce pleaded guilty to take responsibility for his actions and that he hopes to turn his life around.
"He just was young and engaged in really bad behavior. And in this short spate of time, it just sort of spiraled around on itself," he said.
Drug use also played a role in the crimes, Marshall said.
Last month, a jury found Royce guilty of a fifth home invasion robbery. He was convicted of robbery, burglary, firearms violations and reckless endangering.
The robberies occurred during a three-week period in September and October 2005.
"Basically, he was driving around looking for fancy cars, nice homes and picked certain ones of them for home invasion," Arrisgado said. "Fortunately, no one was killed, because he was always armed with a (semiautomatic .45-caliber pistol)."
Royce broke into the Holloways' home in the early-morning hours through window louvers. He threatened the Holloways, took their wallets, including their credit cards, and drove off in their Mercedes-Benz, Arrisgado said.
"They were just scared. They thought they were going to get killed. This guy was very vicious and had no hesitation in pointing the gun in their face," he said.
Marshall said Royce did not know Holloway was a TV star until after the robbery. Holloway plays "Sawyer" on the ABC castaway drama, which is filmed on Oahu.