ΔE 26.5, loose: different enough that you should pick on purpose. Iridescent Gold (Fine) is noticeably lighter than True Brass. They are different kinds of paint: Army Painter True Brass is a metallic and Golden Iridescent Gold (Fine) is a pearl paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 26). Iridescent Gold (Fine) is noticeably lighter than True Brass. They are different kinds of paint.
The same difference applies the other way round: True Brass is noticeably darker.
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.
See True Brass on the colour wheel See Iridescent Gold (Fine) on the colour wheel
All matches: True Brass equivalents · Iridescent Gold (Fine) equivalents