15 µF at 4 V — a standard decoupling value for 3.3 V rails
The TAJT156K004RNJ: This is a 15 µF, 4 V rated tantalum capacitor from the TAJ series, molded case, surface-mount in a 1411 (3528 Metric) / 1210 footprint.
ESR and temperature range — the bench-level limits
The 2 ohm ESR is the number that matters for ripple voltage and self-heating. At 15 µF and 100 kHz, 2 ohm ESR dominates the impedance; the cap will run warm if the ripple current is high.
Active production — no end-of-life clock ticking
No last-time-buy window is open, no successor has been announced.