A debug version of your app is meant to be optimized for that- even if that means adding extra logs (from the system or from your app), systems to catch errors, data tracking and management, everything you can access from the debug menu, and much more.
However, when a release apk is made, it doesn't need all those features. Furthermore, there are speed-related optimizations that can be made to the app by the compiler, which stop you from normally debugging. Thus, it tends to be faster/more responsive- although the varying degrees of improvement depend on what your app is actually doing.