ΔE 28.2, loose: different enough that you should pick on purpose. Pecatum Flesh is noticeably darker than Seraphim Sepia.
Can I use Pecatum Flesh instead of Seraphim Sepia?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 28). Pecatum Flesh is noticeably darker than Seraphim Sepia.
Can I use Seraphim Sepia instead of Pecatum Flesh?
The same difference applies the other way round: Seraphim Sepia is noticeably lighter.
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.