<< your question seems misleading as the 15000 rpm seagate has 3.6 access time so what are you asking whats the next lowest or next harddrive comming out with 15000 rpm spindle speed? >>
Currently, there are 4 different 15000 rpm drives:
(1) Seagate Cheetah X15
(2) Seagate Cheetah X15-36LP
(3) IBM Ultrastar 36Z15
(4) Fujitsu MAM
Of these, Cheetah X15 is an older drive. The second-generation 15K drives outperform it now. IBM 36Z15 appears to run too hot, and shows lower performance, at least according to the reviews. Cheetah X15-36LP and MAM vie for the title of the fastest hard drive on the planet. X15-36LP appears to be a better all-around drive, while MAM shows a slightly better performance with databases.
Leo