ΔE 19.1, loose: different enough that you should pick on purpose. Ink Sepia is noticeably darker, much more muted, cooler than Brown Ink.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Ink Sepia is noticeably darker, much more muted, cooler than Brown Ink.
The same difference applies the other way round: Brown Ink is noticeably lighter, much more saturated, warmer.
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 Brown Ink on the colour wheel See Ink Sepia on the colour wheel
All matches: Brown Ink equivalents · Ink Sepia equivalents