It is regarding the sales of real property so that common law applies intead of uniform commercial code.
Also note that you have already had a valid contract so that the dispute is regarding the performance of the contract.
First, read your contract carefully to see if there is any clause about restitution on late closing or revocation of the offer, such like what the buyer did. If so, that would be the legal basis for your claim.
Second, read your contract carefully to find out if there is any clause about their getting a loan, especially the wording of the contract. Does it use any like "provided, conditioned". If so, their getting a loan is an expressed condition subsequent to the buying, which means that if they could not get a loan then the deal is off. Most courts will consider this as condition subsequent anyway. That, however, does not mean you don't have any restitution. At common law, the contract should be viewed such as the buyers have to pursue a loan with their good faith efforts. Did both of them, the hu*****and and the wife, signed the contract? I am not sure they could not get a loan only because of the wife's bad credit. You said that you know they were lying. Then, you have the burden of proof that they are. Evidence might include such that how many banks they went to and how many refuse to loan them. You have to get the proof and you can not ask them to show the evidence.
Third, did their attorney give a satisfaction? If their attorney was "dissatisfied" then it is final and absolute. They can back off the deal at anytime if the contract calls for satisfaction by the attorney.
Fourth, did the contract call for buyer's satisfaction? Buyer could be also dissatisfied and back off the deal, provided that they are acting in good faith. I would think that you need to gather evidence to show that they actually bought another house in the same locality for less money, or something like that.
Finally, your restitution. Your $15K is based on future expectancy not real damage. Most courts would not consider compensating for future expetancy, unless it is something like stock, which two days might be too long already. In your case, you still have the house. Real damages incurred, such as moving expense, this house sale preventing you to accept a job and move to another location, or something like that, would be considered in court. The basic idea of contract law is to prevent unjust enrichment and impoverishment. You may be losing the $15K due to the delay but the buyer did not get the money. There is no basis for that claim.