Your example is based on everyone working at mcdonalds in oz makes $15 per hour....which is the only theory I am seeing here.
National minimum wage for adults
Currently the full-time minimum wage is
$16.37 per hour or
$622.20 per week. This means that most employees in the national system shouldn't get less than this.
Casuals covered by the national minimum wage get an extra 24% ($20.30 per hour).
National minimum wages for apprentices, juniors & trainees
There are special national minimum wages for trainees, apprentices and juniors who don’t have an award or agreement. From 1 July 2013 these are:
Juniors:
[TABLE="class: FairWorkTableStyle2"]
[TR="class: FairWorkTableStyle2TableHeaderRow"]
[TD="class: FairWorkTableStyle2TableHeaderFirstCol"]Age
[/TD]
[TD="class: FairWorkTableStyle2TableHeaderOddCol"]% of national minimum wage
[/TD]
[TD="class: FairWorkTableStyle2TableHeaderLastCol"]Minimum hourly rate
[/TD]
[/TR]
[TR="class: FairWorkTableStyle2TableOddRow"]
[TD="class: FairWorkTableStyle2TableFirstCol"]Under 16
[/TD]
[TD="class: FairWorkTableStyle2TableOddCol"]36.8%
[/TD]
[TD="class: FairWorkTableStyle2TableLastCol"]$6.03
[/TD]
[/TR]
[TR="class: FairWorkTableStyle2TableEvenRow"]
[TD="class: FairWorkTableStyle2TableFirstCol"]16
[/TD]
[TD="class: FairWorkTableStyle2TableOddCol"]47.3%
[/TD]
[TD="class: FairWorkTableStyle2TableLastCol"]$7.74
[/TD]
[/TR]
[TR="class: FairWorkTableStyle2TableOddRow"]
[TD="class: FairWorkTableStyle2TableFirstCol"]17
[/TD]
[TD="class: FairWorkTableStyle2TableOddCol"]57.8%
[/TD]
[TD="class: FairWorkTableStyle2TableLastCol"]$9.46
[/TD]
[/TR]
[TR="class: FairWorkTableStyle2TableEvenRow"]
[TD="class: FairWorkTableStyle2TableFirstCol"]18
[/TD]
[TD="class: FairWorkTableStyle2TableOddCol"]68.3%
[/TD]
[TD="class: FairWorkTableStyle2TableLastCol"]$11.18
[/TD]
[/TR]
[TR="class: FairWorkTableStyle2TableOddRow"]
[TD="class: FairWorkTableStyle2TableFirstCol"]19
[/TD]
[TD="class: FairWorkTableStyle2TableOddCol"]82.5%
[/TD]
[TD="class: FairWorkTableStyle2TableLastCol"]$13.51
[/TD]
[/TR]
[TR]
[TD]20
[/TD]
[TD]97.7%
[/TD]
[TD]$16.00
[/TD]
[/TR]
[/TABLE]
http://www.fairwork.gov.au/PAY/NATIONAL-MINIMUM-WAGE/pages/default.aspx