ΔE 15.5, loose: different enough that you should pick on purpose. Cobalt Bluegreen is noticeably lighter, more muted than Turquoise Siren.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Cobalt Bluegreen is noticeably lighter, more muted than Turquoise Siren.
The same difference applies the other way round: Turquoise Siren is noticeably darker, more saturated.
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 Turquoise Siren on the colour wheel See Cobalt Bluegreen on the colour wheel
All matches: Turquoise Siren equivalents · Cobalt Bluegreen equivalents