It depends. It could be under a different name but most often the name of the decedent is part of the name. If you have no knowledge of a 'trust' being established with the IRS, and you have know way of obtaining that information, you could apply for an Tax ID for the trust yourself. It's not a concern since it has been 15 years since your father's death.
You can use the link below to apply for a federal tax identification number to file an estate return as administrator.
This number will be used to file Form 1041 which will distribute any income to all beneficiaries. You may want to check with an estate attorney for any details about how to handle the estate at this time.
We are sorry for your loss.