You don't seem to be gaining much from this, at least in JavaScript. The Jatha small LISP library that hasn't been updated since 2007 returns factorial(32768)

You don't seem to be gaining much from this, at least in JavaScript. The Jatha small LISP library that hasn't been updated since 2007 returns factorial(32768) in 5 seconds on a middling machine. (Disclosure: I'm the author of Jatha)