bank account

At the moment you have money in an account that gives interest, you get already taxed. The bank withhold the tax you have to pay for interest income. Before you get to pay for 'patrimonio' you will have a lot of money in your account, which you shouldn't have never more than the 100.000€ that are garanteed in case of bankrupcy. In spite of what they want you to believe, the banks in Spain aren´t very healthy, and by no means able to survive another big recession, at least not all.

Can you tell me roughly how much they tax on £15000 Euros? I need to know than

Ask your bank, it depends on how much interest it generates