I see many going on about the Gate 15 transfer in SYD. One very easy was to avoid this is to turn left and take the train. In the morning trains from domestic to international are almost always empty and they run about every 8 minutes. $5.80 to avoid palaver. I know this will not sit well with those who don't like to spend money.
As for the OP I reckon 3:05 between aircraft hours was just about enough to fully enjoy the lounge. (they certainly didn't have a 90 minute connection). Boarding might be called an 1 hour early, but I'm sure someone in F can probably wait a bit before heading to the aircraft. Having said that an 8 am or 8:30 am departure from MEL would've been my go to choice, rather than 6 am. I've done 6 hours in the F lounge (possibly on my second visit so it was still new) - I almost wanted to hang myself by the end.
