Lightning Returns: Final Fantasy XIII Demo—Zaltys [0:17] (no bonuses)
Done without a preemptive strike or Strength bonuses.
Sub-15 seconds is probable with better timing of Light Slash, Strength bonuses on Red Mage (e.g. from an equipped Charged Strike), and/or preemptive strikes in follow-up battles. Also in the latter case, you can opt not to Overclock and simply use Light Slash until your ATB runs out, then finish with a short string of Quick Freeze and Blizzaga. This results in a slightly higher score (about 5000-6000 points) but slightly slower time (about 5-6 seconds).
Here's an 0:12 fight using a preemptive strike and Strength +160: http://www.youtube.com/watch?v=-5y5rbvEDOo&feature=youtu.be
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