If your question is from the employer side, that you have joined an organisation as the Personnel Manager and would like to bring a practice of deducting the PF to statutory ceiling of Rs 15000, then I would say that there is no legal issues in brining the contribution from actual salary to Rs 15000. This is supported by a Supreme Court verdict also in which the Court said that an employer who had earlier contributed on actual salary can reduce the PF contributing salary to Rs 15000 (at the time of verdict it was Rs 6500) and the EPFO cannot challenge saying that PF qualifying salary cannot be reduced.
But in this exercise you have to take the employees in to confidence. Obviously, contribution to PF on actual salary having been accepted as one of the terms and conditions of employment when you change it, you should given them notice, preferably in the prescribed form following section 9A of the Industrial Disputes Act. You can offer the employer contribution lost by reducing the PF qualifying salary in other forms of benefits. Without notice (21 days before implementation) and without taking them in to confidence you should not do it.
If your query is not from the employer's side but as an employee who is not interested in getting your PF deducted on actual salary then it is a policy matter. You need to check what others are doing. Legally, you can very well say that your contribution to PF should be restricted to 12% of Rs 15000 only. The employer would also restrict his contribution accordingly. But why should you require the deduction to be made on Rs 15000 if the employer is ready to contribute it on actual salary?