块 is a classifier word for currency and I believe can be applied to any currency, not specifically Yuan.
In the news you'd only hear 三百一十五 but in general 三百十五 is understood just as well.
I think only the zero is necessary: 305 would be 三百零五. I live in China and I never hear the 一 in 三百一十五 when they say prices. I always hear the zero however.
As Drinc mentioned, it's context dependent-- it's definitely not necessary and not used in most informal/oral contexts.
"315 kuai" should also be accepted. "Kuai" is common usage in everyday speech for both Chinese and foreigners who have lived in China for any length of time.
块 in Chinese usually is a wide signifier for currency in general, not applied to just the Chinese yuan. Other currencies should be accepted as valid answers.
While there are hundreds of currencies in the world, adjusting this for the more common referrals like the dollar would go a long way.
I thought mandarin would be similar with 福建话, we usually say 315 as “三百一五” or "三百十五“,
Why is 15 suddenly yi shi wu instead of just being shi wu. I can understand maybe both are used, but DL marked shi wu as wrong and insists that i use yi shi wu
that's a pity, that we can pick only 315 because there is no other choice it would be better to have more options