There is no automatic prunning of modules or functions. The feature added in 1.15 is around code paths, which brings mix projects closer to how releases are built by excluding everything but explicit dependencies mostly to otp applications. Previously all of OTP would be available for loading on demand.
To get a smaller codebase you’d need to lessen the (number of) applications you depend on, as there’s also nothing manual for pruning code at the module or function level.
