Playing wow classic anniversary.
The actual blink cooldown is 15 seconds. When I use it, my omnibar counts down a 30 second timer.

If i go to "spells" and check the mage area, blink shows as ID 1953 with a 30 second cooldown.
If i look at my bar/spellbook, the ID of the spell is the same, but it shows a 15 second cooldown.