Plane manuals normally state a number with a decent margin for error.

The manufacturer does not know how you are going to set up your plane, so they err on the side of caution.

If you set things up for maximum mechanical advantage, the chances are you would have NO problems with lesser torque servos which are less than the recommended specs...

However it is best to be right in the middle or greater so to speak, to avoid potential problems...

The servo you are looking at is a bit above a micro size servo, but not quite at the mini-size range.

Micro servos go from about 6g to 13g or so in weight while the Mini's are above this.

Why not look at the 16g servos instead?

Your plane should be able to take servos up to 22g weight.