Forward voltage hits 920 mV at the full 15 A load, which is typical for a 170 V Schottky — the trade-off for the higher voltage blocking is a higher Vf than a 45 V or 60 V Schottky of similar current rating. The 20 µA reverse leakage at 170 V is a datasheet maximum; leakage climbs with junction temperature, so at the 175°C max Tj it will be significantly higher. This part is built for the output stage of a high-voltage power supply, OR-ing diodes in a redundant 48 V or 72 V telecom rectifier, or reverse-polarity protection on a 100 V+ bus where a standard 100 V Schottky would be too marginal.
Any stock in the channel is new-old-stock or surplus from franchised distribution that has aged out of the manufacturer's order window.
D2PAK common-cathode — footprint and thermal note
The STPS30170CG lives in a D2PAK (TO-263-3) surface-mount package with an exposed tab that carries the common cathode. The tab is the main thermal path — PCB copper area and via stitching under the tab determine the effective Rth(j-c).