It depends on your 2012 actual income and your 2014 estimated/actual income. You estimated your 2014 income when you enrolled in an ACA marketplace plan.
Individual Plan, non-Medicaid Expansion state, Scenario #1:
2012 Actual Income: $15k
2014 Income Estimate: $15k
2014 Actual Income: $22.5k (<200% FPL)
Premium Subsidy repayment capped at $300 (individual)
Individual Plan, non-Medicaid Expansion state, Scenario #2:
2012 Actual Income: $15k
2014 Income Estimate: $15k
2014 Actual Income: $47k
Entire premium subsidy must be repaid since actual income > 400% FPL.
Individual Plan, non-Medicaid Expansion state, Scenario #3:
2012 Actual Income: $20k
2014 Income Estimate: $15k
2014 Actual Income: $22.5k
Your ACA application in early 2014 would have been flagged for review and additional documentation since the 2014 estimate is more than 10% different than the 2012 actual income on file.