Will my sister's son ever be relased or will he have serve his life in prion?

That's up to the parole board, which has not been kind to people convicted of murder or even accomplice. I suppose he could file a writ to ask why he is being denied parole.

No one on the internet can answer your question. I'm sorry to hear about your sister's son's situation, but asking attorneys to guess isn't going to help. Even an attorney that is very familiar with his case and history would not be able to predict the future. Attorneys online who know absolutely nothing about the background of the case are even more hard pressed to give a useful answer. All I can tell you is that it is legally possible for him to be released now that he has served 15 years. But no one can tell whether that will ever happen or not.

At some point they will parole him as the prisons are incredibly overcrowded.

I represent many lifers at their parole hearings. To get parole an inmate must demonstrate three things: 1) Insight into his crime It's not entirely clear what this is but showing the board he knows the factors that drove him to commit his life crime + showing that he's engaged in programming in prison to eliminate these factors (e.g. if he killed in a drunken rage that he's taken lots of AA classes, if he killed out of anger that he's taken anger management classes, etc.) + showing remorse for the victim, his family members and loved ones goes a long way 2) That he won't be a threat to the community if released In addition to the above, important factors here are lack of a prior juvenile record, lack of a prior criminal record, and a clean disciplinary record while in prison 3) Adequate parole plans He must have both transitional and long-term housing plans plus marketable skills. The key point here is the board wants to see he will be in a stable situation, have a strong support network and be able to make a living so he won't be tempted to return to a life of crime to support himself; and he has many people who can help support him both financially and emotionally to keep him from re-offending.

Just to clarify terms - an "accomplice" is somebody who was not a participant in the crime, but only assisted in some way afterward. The maximum on that is 3 years. It sounds as though he was convicted of second degree murder under an "aiding and abetting" theory if he did something to facilitate the commission of the crime. A sentence of 15-life means that he is first eligible for parole after serving the 15. From there, he is at the mercy of the parole board. Typically, in a denial, they will give reasons, whether it be a lack of understanding of the crime, lack of remorse, inability to conform to institutional rules, etc. Why they denied him - I don't know. He'll have to examine the reasons given to him and see how he can best satisfy the parole board when he comes up against in three more years.

That's entirely up to the Parole Board in their discretion.

Up to board's discretion, but it is difficult to earn parole. A lawyer may be able to help.