Hello,

Only practising JEE advanced last 15-year question paper thrice won't guarantee you the marks, it will only give you an idea about the toughness of the paper or will create an exam-like environment ( if you give it as a mock test). To score 170 plus in your JEE advanced the concept yours should be crystallised clear, and you should have the ability to solve new questions in the examination.

If you start solving JEE advanced questions simply by looking at their solution then you're not on the right path but if you can solve 40-50% of the paper by yourself without looking at the solution then practising 15 years of questions will be beneficial for you, all you need to rectify your mistake, proper revision and keep improving till the end.

Also, don't forget to give mocks from time to time because it is the most crucial asset to score well in the examination.

Hope it helps, all the best.