Nope, its definately 16 - look here:
http://www.ips.gov.uk/passport/apply-first.asp
If you were still 15 when the passport application was received, and also by the time it came to issue the passport, you would be given a child's one. However, if you turned 16 whilst the application was with IPS, and before the examiner had a chance to issue the passport, you would automatically be given an adult one (and thus have to pay the difference etc).
