Although it's not mormally said that way, it would be "quince cientos." I believe it would be more common to say "mil quinientos."
El año de 1500 (mil quinientos) --- (fifteen hundred)Quinientos (five hundred)
215 is said as two hundred fifteen. Note the word "and" does not appear.
'Las siete y quince' or 'las siete y cuarto'.
15.515 = fifteen and five hundred fifteen thousandths.
Fifteen thousand one hundred and twenty
Eight hundred fifteen.
Fifteen hundred-thousandths.
Nine hundred fifteen.
Fifteen hundred-thousandths.
As a value, it is two hundred fifteen ten-thousandths. You could say "point zero two one five" as a number, not as an adjective/determiner.
One thousand five hundred or fifteen hundred.
two hundred fifteen thousand