That's a very astute observation Kevin but it doesn't surprise me at all. I suppose somebody in the Rates & Fares Office in the Finance Dept in Milewater Road just forgot to change it. The whole of Ulsterbus seems to just work on peoples' knowledge and the correct information isn't available to the staff who need it or it is down differently in lots of different places and they don't have any proper centralised computer system to eliminate the discrepancies.You could e-mail francis.mcgrogan@translink.co.uk to complain (Mr McGrogan is the finance manager and would take an interest in the correct route numbers being used).
Re variations on the 15, there is:
Regular services:
15 Downpatrick to Belfast via Bell's Hill (i.e. direct)
15A Downpatrick to Belfast via Annacloy
15B Downpatrick Town Service (Flying Horse service)
215 Downpatrick to Belfast Express
One journey daily weekday mornings 0655:
215A Downpatrick to Belfast Express via Annacloy
One journey weekly Sunday evening 1915:
15E Downpatrick to Jordanstown Express
15, 15A and 215 are the only ones you would ever see on the destination displays on buses. 15B is always shown as 15 and the others as 215.