The procedure known as NPI, which stands for "New Product Introduction," often takes place during the first three months of each year. This allows Apple to evaluate how well the real manufacturing is going once the new iPhones have been completed.
Apple has begun producing iPhone 15 prototypes in China for testing purposes. It has been reported that Foxconn has begun trial production of iPhone 15s, and the goal of this important step is to settle concerns that have arisen between all of the stakeholders engaged in the process. This involves testing new machinery and changing the quality assurance procedure, in addition to include manufacturers and suppliers in the process.
In addition to beginning the NPI process, the article states that Apple intends to narrow the gap between production schedules in China and India. This will be accomplished by launching the NPI process. Apple began real manufacturing in China six to nine months sooner than it did in India. This is the case as of right now. As Apple continues to focus on forming partnerships with Indian partners, this is likely to alter in the near future.