Netflix voucher card 15 euro

For example, if I get a voucher card for netflix at the gas station! For example, for 15 euro. How many months can I watch then? Do I have to enter the code every time? Or once?

You enter the code once and then you get a Netflix credit which in your case is likely to last for about two months if you have a single account. After that you have to top it up with a new card

So with a 15 euro voucher I can easily watch up to 5 series every day? A good 1-2 month

Sure, there's no limit to how much you can watch in a day.

So if that's a little more than a month, is that a little cheaper than constantly 11.99 from the account?

Well that depends. If you pay from your account, you have a permanent subscription for many months. But if you pay with the gift card you would have to renew it every time, which is quite impractical in the long run. So if you only want to have Netflix for a two month period, I think it's cheaper to take the card. But if you want to have Netflix permanently, the account option is cheaper