This subject isn't a very hard one.
Once you start noticing you aren't losing marks because you don't know something, do a paper or two more, if that continues, i'd just stop.
(This happened for biology... i did a paper corrected it, noted what i got wrong, learnt it, continued to another paper, repeat the cycle. Eventually i found i wasn't losing marks because i didnt know but because my wording wasnt clear or i made stupid mistakes. You can't really fix these things by just spamming more exams)
The gain you'd get out of doing additional papers is small.
The gain you get out of the first 5 is probably pretty big after that it kind of lessens with each passing exam.
I'd spend my time on other subjects at that point (Or if IT is your only subject do as many as you can... don't do what i did in year 11.... i didn't know we were meant to do practice exams... i walked into that exam having done half a exam...suprised i fluked 37)
I still think you'll see very minimal benefit out of 15+ for a subject of this nature. There is only so many things they can ask really and its hard to get creative with the actual concepts themselves like they can for chemistry or math, they can wrap a creative story around a concept for this subject... still the same concept.