ΔE 14.8, fair: the same colour family, but not a straight swap. Light Phthalo Green is noticeably lighter, more saturated, cooler than Leviathan Light.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 15). Light Phthalo Green is noticeably lighter, more saturated, cooler than Leviathan Light.
The same difference applies the other way round: Leviathan Light is noticeably darker, more muted, 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 Leviathan Light on the colour wheel See Light Phthalo Green on the colour wheel
All matches: Leviathan Light equivalents · Light Phthalo Green equivalents