Since August 2017, the official return on Prize Bonds is 0.5%. In practice, you have to look at the return in €50 prizes only which is 0.27% (or 0.28% if you include €100 prizes). These are the only ones you have any realistic chance of winning. By the way, for your €15k investment this means less than one €50 win per year on average, and the lumpiness means you run a significant risk of no returns at all if your time horizon is less than several years.
With DIRT rates set to fall to 37%, the grossed up equivalent interest rate in a bank account incurring DIRT is 0.43%. If you look at the Savings Best Buys thread, there are some accounts paying better than this. Your experience may vary, but I don't think buying and encashing prize bonds is any less hassle than opening a bank account.
(It's gotten to the stage where personally I don't find the rates on any account attractive enough to be bothered moving from my current provider which just happens to be Rabo, even though their rates are in the basement).