Hi,
This particular "perquisites" part of the salary is governed by the Income Tax Act. Here, the amount is not taxable if reimbursed by the Employer to the Employee up to INR 15,000 per annum. The word "reimbursement" itself suggests "compensation paid when a claim is made," and here a claim always has to be supported with some evidence of expenses, such as bills, etc.
I cannot say I have spent INR 15,000 on medical treatment, but certainly, I need to prove it with certain documentary evidence. As Fringe Benefit Tax (FBT) has already been abolished, I believe it will be as per the provisions mentioned in the Income Tax Act under the head Salary - Perquisites.