In the past month I've bought two cheap books at 99p, borrowed two library books, and splurged a whole £2.50 on a book I've been waiting for nearly a month to drop from £3.66 (and I'm still annoyed I missed getting it for the £2 it was for 24hrs one day before I bought it).
You really need me to sit on your shoulder and constantly remind you of why you started this thread....
Of course you'd soon get fed up of my thriftiness and brush me off your shoulder and frantically grab all the books I'd stopped you from buying.
Good luck with your £15 budget. Go on, you know you can do it!