If I am not mistaken, any JVM language that has immutable data structures and closures is probably going to generate a fair bit of garbage. I believe this also applies to using Scala functionally.

My understanding is that there is greater interest in making Clojure more suitable as a library and with a leaner runtime requirement. If you have a situation were you don't need a dynamic environment, having the option to compile functions to static methods instead of classes should result in a big performance increase.

I have only briefly looked at Kawa Scheme, but I have not had the time to do much with it beyond a "Hello, World!" sort of project. Mirah is another interesting option. It uses a Ruby-inspired syntax but requires no runtime library.