I agree with the 15M value as I perceive that Bitcoin loss would keep happening even after halving.
What do you mean by "even after halving"? You know that this is neither the first nor the last halving?
Very correct. Evaluating the number of lost coins can be very difficult, and it would be also wrong to think that all inactive wallets that holds Bitcoin are long lost. Recently, a long inactive wallet just made a transaction, which means it is certain that others might still safe.
Wait, a minute ago you were cool with a value of a 15 million Bitcoins? Whats that based on? You literally just admitted it is hard to estimate this thing!