Good evening,
I am assuming you have seen the building, if not I have attached a picture. It is a 3 story block of flats and 15 is behind the bush or just above it. Depends on whether there is a no 13 or not.
Looking at them they could be pre or post war, difficult to tell with this style. They were still built into the 60s.
John915
Added, Had to look at several estate agents before I found one that gave a date, but built in the 30s. 192.com lists a no13 so 15 is the one on the first floor above the bush.