I remember when people used to say having 21 was good, because then you would have 1 millionth of the supply. Now I see people talking about some 6.15 number, which I have no idea why or how anyone came up with that number.
Can I ask you a counter-question? What do you think the possible price of 1 BTC will be in the future, 5-10 years from now and how much money you consider a sufficient amount?
21 is just because of a total
BTC supply of 21 million, there is nothing special in that number, and 6.15 is probably 6.25
BTC which will be reward for one mined block after next halving, you mixed up some things.
I would like to have at least 10
BTC one day, and I would like to see the value of 1
BTC at $100 000 which would mean I would have $1 million, but that does not mean that I would not be satisfied with 5
BTC.
It is not easy to buy or get in any other way 1 whole
BTC, there are countries where wages are very small, and people barely survive. For them, even 0.10
BTC is a difficult task. Some others are more fortunate to live in richer countries, so it is much easier for them to reach that goal.