But overall, reusable bags need to be used at least 50 times in order for their environmental benefits to be realised. http://www.abc.net.au/news/2017-05-24/war-on-waste-what-bags…
But from the experience in my family, some of bags were already ripped, stretched and had holes after one single use. I haven't put any heavy items or sharp objects yet. Maybe a box of tissue is too sharp for them. I highly doubt these bags are able to sustain 10 uses.
Some other shops simply provide the "same" plastic bags except they are thicker than 35 microns and customers have to pay for them. I also doubt these bags cost more than 15c than the old "single use" bags to the merchants.
It is true that the 15c cost will discourage people from using them but more people still do. As long as one in 50 customers uses it as disposable bag, the benefits to the environment will diminish.
So the result of the bag ban is we the customers now pay more to do more damage to the environment, and merchants and overseas plastic bag suppliers pocket the windfall.
In general the average number of uses of these bags is likely to match, or be less, than their environmental breakeven point. For those 15c bags the breakeven is going to be around 10 times, but so is the average usage (single uses will really hit the average). A cotton bag will last longer, but the breakeven is much greater (in the hundreds of reuses)
And then you have the bin liners that will have to be bought.
Cutting the plastic packaging would have had a much bigger impact, but there was a bandwagon to jump on.