15 days is a very little time, I am providing here the topics which covers the most weightage as per the past year observations, study those as per your choice:

Physics:

• Modern Physics
• Heat and Thermodynamics
• Optics
• Unit, Dimension and Vector
• Kinematics
• Electrostatics
• Current Electricity

Chemistry:

• Transition Elements and Coordination Chemistry
• Periodic table and Representative Elements
• Thermodynamics And Gaseous State
• Mole Concept
• Nuclear Chemistry And Environment

Mathematics:

• Coordinate Geometry
• Limits, Continuity and Differentiability
• Integral Calculus
• Complex numbers and Quadratic Equation
• Matrices and Determinants
• Statistics and Probability

For more information regarding the JEE MAINS chapterwise weightage consider the link below:

https://engineering.careers360.com/articles/jee-main-syllabus-weightage

I hope this helps. Wish you a great day!