ΔE 17.8, loose: different enough that you should pick on purpose. Mephiston Red is noticeably darker, warmer than Space Red.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Mephiston Red is noticeably darker, warmer than Space Red.
The same difference applies the other way round: Space Red 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 Space Red on the colour wheel See Mephiston Red on the colour wheel
All matches: Space Red equivalents · Mephiston Red equivalents