Not sure what you are trying to do. You cannot "file a 15 year old W-2" for a tax refund. You are too late to receive a refund for any tax year earlier than 2017 ( and even that is very iffy).
If you have a W-2 for 2020 you can put it on a 2020 tax return -- or if you are now working for an employer who will issue a W-2 in January for 2021 you will put that on a 2021 tax return next year.
W-2's come from your employer. If you worked in 2020 and did not receive your W-2 then contact the employer to ask for another copy.
Oh----do you mean you have a teenager who worked for the same employer you worked for? You do not put your child's income on your own tax return. The teenager can file his own tax return if there is an amount in box 2 of his W-2 in order to get a tax refund. He has to say in My Info that he can be claimed as someone else's dependent.
But if you are the one who needs to file a tax return, you need to get your W-2 from the employer.
only the Social security Admin would have a copy of a 15-year-old w-2. as stated if you want it so you can get a refund form that year you're too late. if you need it for some other purpose see this link