"They say" you are, or you are?

You DID NOT sign a union contract at 15. There isn't a union on the planet that would allow a minor to join.

As you ARE lying about the BASIC facts of the case, AND you didn't actually ask a question, the answer you want isn't true.

I am not sure that you can start at 15 to be vested, check with your local state representatives office.

You signed a union contract at 15? Not believable!

Well, work the 3/4 of a year then.