It seems that production of the fastest 15k rpm HDDs are on the decline, Toshiba sees no reason to release news HDDs with that rotational. In a news-item website Golem reports about this news, there is not enough demand for fast HDDs due to to the rising demand of SSDs.

Toshiba currently has six 15k rpm models listed in various pricewatch engines, the largest capacity one is a 600GB model. Larger capacities would have certainly be possible, but Toshiba doesn't see any demand in that as at that performance and volume level the demand for SSDs simply is bigger. Also the price per GB compared to an SSD does not make much sense anymore they state, as such the 15K rpm hard drives are too expensive compared to the significantly faster SSDs. 

HDDs aren't dinosaurs just yet though. It seems it all remains to be different for 10K rpm HDDs, Toshiba will release a new series based on that speed. Currently the maximum capacity for 10K RPM HDDs is 1.8TB. The demand for 7200 rpm HDDs will remain strong they claim, low-perf 7200 rpm HDDs are still in high demand even in the server segment as there is a NAND shortage.

Toshiba does mention that a full migration from HDD to NAND storage simply is not an option short term. The storage demand is too high as production capacities are not enough to keep up with the current hard disk business and thus demand. This is one of the reasons why you will have noticed that SSDs have become roughly 20% more expensive compared to half a year ago. There is a NAND storage shortage.

Toshiba Will Not Release New 15K RPM HDDs