FHSS Question and first time home buyer

Hi people! I am about to purchase my first. I have around 15% of deposit saved and was wondering the next. We all know about FHSS, and how we are able to contribute extra to our super and then pull out those contributions for deposit. Additionally, we can put extra contributions for previous years too (I think it goes 5y back right?). I know max contribution for FHSS per year to pull out is 15k. Now my question is, can I contribute all 15k for past 5 years (for each year) so something like 75k this week, and then reduce my Tax (get some money back as refund at EOFY) and then "walk"into bank second week and say that I will be using that 75k of extra contributions for deposit?

Does this make sense? and is it doable?