"what should the answer be for "Total Deductible Medical Costs" line 14 of the Medical Costs Worksheet (which flows to line 1 of Schedule A)?"
$15,000.
When asked, "Tell us about any other medical expenses," make sure to enter $700 for 2024 qualified medical expenses paid from the HSA in 2025. TurboTax subtracts the entire amount paid from the HSA, not just the part of the HSA distributions used to pay 2025 expenses (because TurboTax has know way to know the breakdown).
