Hm, did you copy the Manifest.toml file over? Try using Pkg; Pkg.status("CUDA") on both versions to see if you get the exact same version.
It looks like CUDA.jl updated the artifacts 11 days ago (https://github.com/JuliaGPU/CUDA.jl/pull/530) to “CUDA 11.1 update 1” (from “CUDA 11.1”), so I suspect you have a slightly newer version of CUDA.jl in your 1.5 environment that is downloading the updated artifacts.