Seriously 15k is going to be far difficult to live and survive on
Seriously, it isn't. Look at all the students living in London for a start.
If anyone has the following
Cheap meals to make.
Cooking books
Good places to shop for food in london.
first two, get a student cook book
second - depends where you live
you seem to have missed the point that London is a big place, I don't think you've actually said what area of London you'll be working in - if you did that it would be easier for people to suggest areas to live in