Release from prison (on licence) is usually at the half way point of the sentence, so that makes the total time in prison approx 228 days. (I've assumed that 15 months is calculated as 1� x 365 days). Therefore the person should be released after a further 20 days in prison. However the actual release date might be a bit earlier because:
(a) 'police days' (i.e. any days when the offender was required to attend a police station) can be deducted from the sentence ; and
(b) prisoners aren't released at weekends. If their nominal release date is a Saturday or Sunday they'll actually be released on the preceding Friday.
Chris