ΔE 15.9, loose: different enough that you should pick on purpose. Midnight Purple is noticeably darker, warmer than Blue FS15044.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Midnight Purple is noticeably darker, warmer than Blue FS15044.
The same difference applies the other way round: Blue FS15044 is noticeably lighter, cooler.
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 Blue FS15044 on the colour wheel See Midnight Purple on the colour wheel
All matches: Blue FS15044 equivalents · Midnight Purple equivalents