He said the jail was one of the worst in the world.
"I think he's going to have a hard time."
Mr 'Ilolahia, who has visited people in the prison several times, said the jails in New Zealand were "five-star" by comparison.
"I've spoken to guys who have been in jail in Tonga and then come and spent time in Mt Eden [prison]," he said.
"They say Mt Eden is five-star - and that's saying something."
However, the brother of a man killed in the ferry sinking said the five-year sentence was disappointing.
Elvis 'Elone of Auckland, who lost his younger brother and a cousin in the tragedy, said: "If it was only one person [who died] then yeah, it's okay.
"But 74 people died, so it should be five times 74 - then it'll be fair.
"When I first heard he got five years, I just laughed to myself because he must be laughing - he got away with it."
Mr 'Elone's brother Sione Valele 'Elone was on his way to the island of Ha'apai to get married when the Princess Ashika capsized.
He was accompanied by his cousin Sione Veuveuso, who was to be a witness at the wedding, and by his best man, Sione Aho, a former North Otago rugby player.
All three men perished.
The Princess Ashika's captain, Maka Tuputupu, was handed a four-year jail term after being convicted of manslaughter by negligence and of sending an unseaworthy ship to sea, but will serve only six months.
Viliami Tu'ipulotu, a former director of Tonga's Ministry of Transport, was handed a three-year suspended sentence after also being convicted of manslaughter and sending an unseaworthy ship to sea.
First mate Semisi Pomale was jailed for five years for manslaughter but will serve 18 months.
