ΔE 14.8, fair: the same colour family, but not a straight swap. Nurgle's Rot is noticeably darker than Matt Bile Green. They are different kinds of paint: AMMO by Mig Matt Bile Green is an ink, glaze or transparent paint and Citadel Nurgle's Rot is a technical paint or medium, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 15). Nurgle's Rot is noticeably darker than Matt Bile Green. They are different kinds of paint.
The same difference applies the other way round: Matt Bile Green is noticeably lighter.
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 Matt Bile Green on the colour wheel See Nurgle's Rot on the colour wheel
All matches: Matt Bile Green equivalents · Nurgle's Rot equivalents