> I feel silly for even mentioning this, but there are less than 256
> countries in the UN, and as far as I know, each has at most one
> currency, so you could use 8 bits instead of 15.
>
That's not always true, e.g. China has RMB and HKD. Also Taiwan is not a
member country of UN but I don't think one would exclude TWD.
There'll also times a country may transit from one currency to another.
Even a currency (currency of most continental European countries before
Euro) is no more being used, it may still need to be supported.
xz