Direct tax and indirect tax

Depends on your maintenance of consistentcy and intent and capability
My suggestion is
Daily 12hrs study. DT and IDT each 6 hrs. Read only ICAI material and past 2 attempt question papers, RTP, MTP.
Read ICAI material from most important chapters to least imp so that if time is not sufficient then you can do atleast sums in material for chapters which you will read in last and that will be least imp chapters
And remaining hrs after reading DT and IDT read or revise other subjects. don't leave them otherwise you may forget...depends on your memory power

15 days are very much sufficient to prepare tax subject. Daily read one chapter from gst and first complete heads of income.then u will get confidence and then complete remaining dt chapters.while preparing write all the imp points that confuses u nd at the time of exam u may recall them

allot more time to DT and less time to IDT as IDT is easier than DT
3 complete days are suffient for IDT
rest of days ,you can do DT

its Simple.... kindly watch vijay sarda lec...on YouTube...ll be available to finish ur DT in a day....and for gst vishal battad or mahesh gaur...or rahul garg.... please do check the notes also...that are also updated....on there website