I'm not seeing that on my local machine? Were you comparing on the Playground which would be quite variable in its results?

    > cargo build
       Compiling foo v0.1.0 (/private/tmp/foo)
        Finished dev [unoptimized + debuginfo] target(s) in 0.42s
    > ./target/debug/foo
    drop in another thread 52.121µs
    drop in this thread 514.687233ms
    >
    >
    > cargo build --release
       Compiling foo v0.1.0 (/private/tmp/foo)
        Finished release [optimized] target(s) in 0.47s
    > ./target/release/foo
    drop in another thread 48.418µs
    drop in this thread 548.005373ms