Hi,

No, There is no such notification is released on the official website of nta neet exam regarding the increase of all candidates marks by 15 in neet exam.

As the provisional answer key has been released by nta neet. Candidates can challange the answer key if they found any wrong questions or answer.

If the nta neet accept the challange is correct. In that case it might be possible that student can get the extra marks.

However until the final answer key releases we can not surely say that nta will add some marks of all neet candidates or not.

Hope it helps.