How long does it take on average for the IRS to say ok to the sale of a house with a tax lien?

We are trying to buy a house and the title search showed many tax liens by the IRS. Turns out the sellers won’t net enough to pay the lien. We have verbal assurace that the IRS has agreed to the sale, and the sellers submitted all the paperwork. But how long does it typically take for the IRS to respond? The IRS told the title agent a min of 15 days. Does anyone have any experience with this?
So, we didn’t know about the liens untill the title search. We were told the sellers finally submitted all their paperwork to the IRS. The title agent has spoken to the IRS personally. The sellers owe more than they will clear. So, do I count 30 business days after they turned in all the paperwork? They’ve already had to pay for one extention to our loan lock.

15 days? In your dreams! The seller will have to submit an Application for Discharge of Property from Federal Tax Lien. Putting the application together is no cakewalk. I recommend to my clients that it be done as soon as escrow is opened because it ordinarily takes at least a month to get approved. If you make the requests 15 days before closing it is not going to be done and the sale may fall apart. IRS generally has a backlog and everybody wants theirs done yesterday so don’t ask to jump to the head of the line.

UPDATE: Plan on a wait of at least 30 days from the time the application for discharge was submitted.