It is okay as long as the PF qualifying wages are not less than Rs 15,000. However, it is always good to take an undertaking from the employee that the reduction of PF contributing wages is as per their choice and understanding. There is no formal format for it, but you can draft it like this:
"I have been contributing to PF based on my actual basic salary. However, starting from this month, my EPF contribution shall be limited to the statutory amount, i.e., 12 percent of Rs 15,000. I also give permission to the employer to contribute their share at the same rate as mine."
This type of undertaking may prove useful in the future to avoid situations where employees claim their PF accumulation is insufficient due to lower contributions. Additionally, if the EPFO or courts decide that pension calculations should be based on higher wages and PF contributions, employees might hold you responsible for not contributing based on the actual basic salary rather than the Rs 15,000 limit.