If you are asking how many hours driving lesson you should have on the day of your practical car assessment with the DSA examiner, I want you to know that 1.5 hours is too much and could affect your ability to pass the driving test.
Most driving instructors will pick you up about 1 hour before the test, and this time is normally utilised just to get you used to the driving conditions on the day, and practice one or two test maneuvers, go over some of the show me and tell me questions you might be asked, and is thus not the time to be learning anything new (its too late for that).
You do not want to arrive for your driving test exhausted or worn out because you've just had a 2 hour session with your instructor. You need to be fresh and able to concentrate, so don't book a 1.5 hour lesson before arriving at the DSA test centre.
Important! If you are not learning to drive with an instructor, it is important that BOTH you and the person teaching you to drive read The DSA official test guide, this book will greatly increase your chance of passing the driving test without spending too much money on lessons.