Just to confirm the maths...
3% to cover the period 1 July 2016 to 30 June 2017.
3% to cover the period 1 July 2017 to 30 June 2018 and
1.5% to cover 1 July 2018 to 31 Dec 2018. (it is just half a year therefore half the rise)
The last one is NOT a 3% annual payrise.
Let's assume you earn a nice round $104000 per annum ($2K a week) to make the maths easy.
July 1 2017 you get a 3% pay rise so your annual pay becomes $107,120 or $2,060 a week. Calculating the cross check from $2,000 a week with a 3% rise you get $2,060 for each and every week of the year.
Now, looking at July 1 2018 let's look at 1.5% for the first 6 months. Your pay would be $104,000/2=$52,000+1.5%=$52,780. If you then get a further 1.5% for the second half of the year you get $52,780+1,5%=$53,571.70. Total for the year $106,351.70.
Net difference = $107,120 - $106,351.70 = $768.30 less.
Alternatively it could be seen that you get an annual pay rise of $2,351.70 on your initial $104,000 which is a pay rise of 2.26%.
The reason for the differential is in the first 6 months you are only getting half the pay rise so you would need a larger percentage rise in the second half to compensate for the 6 months during which you only received 1.5% extra.