ΔE 15.0, loose: different enough that you should pick on purpose. Copper Coin is much more saturated than Balthasar Gold.
Can I use Copper Coin instead of Balthasar Gold?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Copper Coin is much more saturated than Balthasar Gold.
Can I use Balthasar Gold instead of Copper Coin?
The same difference applies the other way round: Balthasar Gold is much more muted.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.