Generally, Yes, we should provide a risk report. But in your particular case, you should NOT.
We categorize risks in following two categories:
2. Customer shared
So,We maintain a risk register and whatever risks we see; should be communicated to customer, we share the risks falling under Customer Shared category with customer in calls/meetings.
But, we do it well in time.
And we also share the mitigation and contingency plan for the risks.
What's wrong with your case?
In your case, the problem is that, risks have not been shared with the customer in a timely manner and now when only 15 days are left for the project delivery, you want to share the risks with the customer. This is not a good idea. Client would be furious because this is a blunder from your project side.
What should you do?
I would not suggest you to hide the facts from customer. But don't share a formal risk report with the customer now. Try to fix whatever you can in whatever time is left in the project delivery and informally; during meetings and calls; try to give the customer some idea about the problems. Do not set a meeting or share a document at this point in time. It will be disaster. All your focus will shift towards pacifying the customer when your main focus should be to bring the project back on track.