15 days are a lot more than you need if you are only trying to prepare for the aptitude round. For the technical rounds, you need a lot more time.
For Aptitude you can start with R.S Aggarwal’s book and then move to the LOD1 of Arun Sharma. That should be more than enough to get you through.
Also, try to attempt mock tests of companies based on last year’s patterns. You can find most of them on Amigoz App.