Question is not clear whether construction is completed in FY 22-23 or 1.5cr is only an estimate. The construction cost of a house is important in many aspect in Income tax such as capital gain tax, property tax, home loan interest deduction, calculation of rental income etc. 
Some aspects of taxation, such as capital gains tax, are calculated based on the actual construction cost, which is determined after the construction is completed. However, the estimated construction value can still be relevant and necessary for several reasons, even before the construction is finished. Here’s why:

1. Property Assessment: Local municipal authorities may assess property tax even before construction is completed. In such cases, they rely on estimated construction values to levy property tax on properties that are under construction. These estimates help determine the potential value of the property when it’s completed, and taxes are assessed accordingly.
2. Home Loan Approval: When you apply for a home loan to finance the construction of a house, the lender may require an estimated construction value as part of the loan application process. The estimated value helps the lender determine the loan amount you are eligible for and the terms of the loan.
3. Pre-Construction Planning: Having an estimated construction value is essential for financial planning and budgeting during the construction phase. It helps you or the builder determine the approximate cost of construction, arrange for funds, and make financial decisions.
4. Documentation: It’s common for various regulatory and legal documents, such as building permits and property records, to require estimated construction values. This documentation is used for tracking and compliance purposes.
5. Future Tax Planning: Even though certain taxes like capital gains tax are calculated based on the actual construction cost, having an estimate beforehand can help in long-term tax planning. It allows you to understand the potential tax implications when you decide to sell the property in the future.
6. Regulatory Compliance: In some cases, local building authorities may require an estimated construction value as part of the approval process for construction projects. This helps ensure that the project complies with local building regulations and codes.

Hence It’s important to maintain accurate records and documentation throughout the construction process to ensure compliance with local regulations and to facilitate future transactions and tax calculations.