if inflation were to stay at the rate it was around 2021 peaks (though it won't), would cut that value in half in 10 years. Also consider that we are almost at the precipice of the technological singularity so how do you know what financial, political, economic systems will look like?

Obviously 1.5M is more than enough to live simply on. But it's more of an existential concern, not a literal math concern unless spending is super high