Yeah, it was 10% for a long time and they bumped it up to 15% back in the ToAU days during a big BP adjustment cap, so it was definitely programmed at a different time than Haste at least.
Confirmed it, by the way.
* SMN/BLM Firaga = 12 seconds with Hastega (15.25*(1024-153)/1024)
* WHM/BLM Firaga = 13 seconds with Haste (15.25*(1024-150)/1024)
Tried each nuke multiple times.
Yet another reminder that any value which hasn't been explicitly tested in FFXI is suspect.
* SMN/WHM Reraise = 51 seconds with Hastega (60*(1024-153)/1024) - excludes 154
* BLU/THF Bludgeon = 9 seconds with Hastega (11.75*(1024-153)/1024) - excludes 152
So yeah, it's 153/1024