The terms you get all depend upon your age, financial circumstances, and the bank you are talking to, so the terms you mention above may not apply. In that respect there are no ‘rules’, other than the one that says it depends upon your circumstances.
Most banks in Spain don’t offer interest only mortgages. Of those that do, it may be possible to find 15-years interest only at 80% loan to value. Once again, though, it all depends upon your circumstances.