I could be reading this wrong however Macquarie Prime...

I could be reading this wrong however Macquarie Prime "collateral" is the amount you have to put up. I am not sure where the 15% and 55% came from, but looking at their site today the collateral you have to provide to buy AVX is 85% and Macquarie Prime will provide the 15%. Macquarie Bank do not provide any % value for AVX in their Margin Lending product.

Collateral
When opening a position, a deposit of collateral is required rather than full payment for the value of the underlying shares. This collateral represents additional security held by Macquarie for your orders and share positions.
The minimum amount of collateral required is based on the market value of your shares and must be maintained throughout the life of the position.

You can see a collateral calculation in this simple diagram.

Share Volume Share Price Share Value Collateral Rate Required Collateral Amount
XYZ 1,000 $30.00 = $30,000 x 5% = $1500

Choose your level of gearing
MQ Prime is a flexible facility that lets you vary your gearing level anywhere between 0 and 95%. For example, the following table illustrates levels of gearing on a $100,000 investment with different cash balances.

Share Value Funding Balance Cash Balance Interest Balance Effective Gearing Ratio
$100,000 -$100,000 $100,000 - 0%
$100,000 -$100,000 $50,000 -$50,000 50%
$100,000 -$100,000 $25,000 -$75,000 75%
$100,000 -$100,000 $15,000 -$85,000 85%
$100,000 -$100,000 $5,000 -$95,000 95%

Gearing gives you the potential to increase the size of your returns by increasing the size of your investments

The greater the level of gearing, the greater the potential returns but this also increases your risk because gearing will magnify any losses. Variable gearing enables you to choose your own gearing risk level.

Stock Code Security Issuer Collateral Rate GSL Offered Shorting Offered CFD Offered
AVX Avexa Limited 85.00% No No Yes