Maybe you're not built to be under 15% body fat? Maybe your body has a larger amount of visceral (fat around the organs) than subcutaneous fat (fat just under the skin). If this is the case then it's actually better for you to stay above 15% as to keep a reasonable protective layer of fat around your organs.
Don't get caught up in just focusing on one specific measure of health mate, body fat %, waist girth, BMI etc all have plus points but are all also flawed in different circumstances.
As long as you don't get out of breath when you have to get off the couch to get a beer from the fridge, all is good! ;-)
Your mind works best when it's like a book, open. ~ Yoda
the question is do you want to be fit or do you want that elusive six pack ;D like everybody has said before a little gut rubber isn't the end of the world as long as your fit aled. but if you take your diet and look at it closely i'm sure you could make a few adjustments, but doing that is boring and hard work and makes you miserable, you ever seen a happy body builder ;D
Life's journey is not to arrive at the grave safely i a well preserved body... but to skid in sideways,totally knackered and worn out shouting....Holy shit!...WHAT A RIDE!!
The 'Gold Standard' is underwater weighing... That said, a well trained and well practised person with a pair of Harpended Calipers can get within 3% accuracy of underwater weighing.
The 'Athlete' bracket is between 4-10% Body Fat (depending on sport, obviously) depending on age group, and also depending on whose train of thought you subscribe to...
The key things with the BIA (Biolelectrical Impedence Analysis) scales you are discussing is that they are not accurate (ie don't represent actual body fat) as they can change with hydration status, electrolyte balance etc, but they can be reliable if you use them at the same time of day / hydration status, allowing them to show a change in readings...
Phew... Happy to answer any questions on BIA / Body Fat %...