Repayment started on the 2010 return + 15 years means you finish paying with the 2025 tax return. Look it up here :
https://www.irs.gov/credits-deductions/individuals/first-time-homebuyer-credit-account-look-up
https://www.irs.gov/pub/irs-utl/oc_fthbc_lookuptoolfinal.pdf
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