An existing 15 year lease is in jeopardy because of the foreclosure that was filed on the commercial property. Will this affect the existing lease?

Possibly but not definitely.

Very often when a commercial landlord finances the property they are required to sign an Assignment of Rents and Leases to the lender. That document automatically assigns the lease to the lender and authorizes payment of rent to the lender in the event of a default by the borrower.

If your lease was assigned pursuant to this document then the lease remains in effect and the lender is your new landlord. You will need to find out if an assignment was done. Unfortunately it's not a document that is normally recorded so there's really no way of knowing if the lease was assigned until you hear something from the new owner.