You need to give us a few more details to replace my guesses about the agreement, but this may not be "credit" (as defined in Section 1026.2(a)(14).
I'm guessing that the agreement calls for the candidate to remain in the bank's employ for 5 years--at which time the full $15,000 will be forgiven. I'm also guessing that there are no fees and that no interest will be charged if the candidate remains employed for 5 years.
For closed-end credit, Section 1026.17(c)(1) tells us to base all calculations and disclosures on the terms of the legal obligation between the parties. If, as I guessed above, the basic agreement calls for the candidate to continue his/her employment for at least 5 years, then all the remaining details about earlier termination are contingencies, not the primary agreement.
Reg. Z's definition of "credit" is "the right to defer payment of debt or to incur debt and defer its payment." When the new hire carries out his/her promise to remain for 5 years, the contract requires no payment of any kind. No payment means no credit, no credit means no consumer credit, and no consumer credit means no Reg. Z coverage.
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...gone fishing.