Most deals of this nature are going to have a sunset clause, this doesn't seem to be a big deal. Before 15 years is up, there's just a new negotiation.
No, most deals have a withdrawal clause, where either party can end the deal.
They don't normally have a set end date.
A set end date basically means Iran plans to restart activities on that date without any kind of sanction. There's a reason this deal was so heavily criticized.
From the text of the deal itself? All the nuclear restrictions were for "15 years", and some for 10 years. After that? Unclear.
Surprised at the downvotes - read the text for yourself: http://www.documentcloud.org/documents/2165388-iran-deal-tex... search for 15 years, it's the plain fact of the matter, not some "talking point".