OT but in the UK a jail sentence for life is for life and a jail sentence for 15 years is for 15 year.
However, on a life sentence you can apply for parole after a minimum period set by a judge (guidelines are set in UK Law but often 15 years minimum). Prisoners may then be released on a life licence but they are still serving there life sentence just not behind bars - consequently breaches to parole will result in a return to prison. Prisoners sentenced to 15 years serve 15 years and then are released without conditions. Whilst some might see it as a technicality - those sentenced to life do serve life, but they are not necessarily in custody for the entire period.
In England and Wales, a life sentence is a prison term of indeterminate length. Formerly, the Home Secretary reserved the right to set the "tariff", or minimum length of term, for prisoners sentenced to life imprisonment, but since 2005 only a judge may set the tariff. The average sentence is about 15 years
before the first parole hearing, although those convicted for heinous offences serve their sentences significantly longer - Ian Huntley was given a tariff of 40 years. Some receive "whole life tariffs" and die in prison, such as Myra Hindley and Harold Shipman; there are currently around 25 people serving whole life tariffs in the UK. Prisoners jailed for life are released on a life licence if the parole board authorises their release.
Life sentences are generally 15 years, but life sentences can be handed out in sets, ie. 3 life sentences, but the above is true