David,
Sorry for not answering your question for so long. I am pretty sure Streeview will work with JS API version 3.15. Well since I am just starting to look at the JS API 4.0, I can't give your a sure answer. However i can't see any reasons why it won't work with version. Google API and JS API are all written in Javascript, they are all about filling html elements(div etc) map content or component.
Let me know if you encounter any issues when you use Streeview with version 4 because i am just as curious as you on this same issue.
Heming