The winter solstice falls in the third week of June every year, the shortest day and longest night on the Australian calendar. 15 June 2030 sits close to this turning point, after which daylight hours slowly lengthen again toward summer, even though winter continues for two more months, through July and August.
A public holiday that falls on a Saturday sits inside the weekend rather than beside it, so it does not automatically create a substitute day off during the working week; whether one applies depends on the specific holiday and the state. Saturday 15 June 2030 falls on this day of the week, inside the weekend itself.
A public holiday that falls on a Monday or a Friday produces a three-day weekend without using any annual leave, which is why long-weekend planning around 15 June 2030 depends on which day of the week the nearest public holiday falls on. A midweek holiday delivers no such automatic extension, though many workers bridge it with a single day of leave.