Oh wow, that's impressive. Depends on how much time you have left, a paper should take about 2 hours 30 minutes for competent students like you, so 15 in a week should be okay if you do 2 a day-ish, though idk when ur trial is, spread them out more if you have time. Though if you're picking up extension 2 in year 12 ur adv mark won't count, but doing well is a good insurance ig in case you end up only doing 3u in yr 12.
There's no better practice than papers out there, I suggest you save the super hard papers like ruse and baulko for last and do any other school's first, mark and find what questions you struggle with, perhaps go to the Cambridge or new senior's textbook and revise them then come back for more. I don't think any subject other than maths have yr 11 content tested in yr 12 so go all out for maths is not a terribly bad idea, by all means it could count to your final ATAR so I don't see any reason to not prioritise it. no worries and good luck!