15 µF at 16 V — the first thing a BOM checker confirms
TAJC156K016HNJ is a 15 µF, 16 V rated molded tantalum capacitor in the TAJ series from KYOCERA AVX. The ±10% tolerance keeps the actual capacitance between 13.5 µF and 16.5 µF, which matters when you are sizing a hold-up cap for a power rail that must stay above the regulator dropout during a transient. The C-case (2312 / 6032 Metric) footprint — 6.00 mm x 3.20 mm with a seated height of 2.80 mm — is a common size for 15 µF at 16 V in the TAJ family. If your existing board has a C-case pad, this part drops in without a layout change.
At 125°C, the 2000-hour lifetime is the rated endurance under full DC voltage. Derating to 80% of rated voltage (12.8 V) is standard practice for tantalum reliability; doing so extends the useful life well beyond the spec sheet minimum.
1.8 Ohm ESR — what it means for ripple and self-heating
For a 100 kHz buck converter with a 500 mA ripple current, the ripple voltage across this cap is about 0.9 V pk-pk — enough that you should check the downstream rail's ripple budget. ESR also drives internal heating. At 125°C ambient, the allowable ripple current is lower than at 25°C; the datasheet's ripple-current derating curve (not reproduced here) is the right reference for a thermal design. If your load current is high, a lower-ESR alternative in the same case size may be needed.