ΔE 27.7, loose: different enough that you should pick on purpose. Ultramarine Blue is noticeably darker, much more muted, cooler than Purple Interference.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 28). Ultramarine Blue is noticeably darker, much more muted, cooler than Purple Interference.
The same difference applies the other way round: Purple Interference 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 Purple Interference on the colour wheel See Ultramarine Blue on the colour wheel
All matches: Purple Interference equivalents · Ultramarine Blue equivalents