Deferred loading. Remove :use and :requires from the ns declaration, as that will load the referred classes recursively in the static initializer of your namespace. Total time spent loading classes doesn't change, but you can amortize it along the perceptions of the user in chunks.

deferred.clj

(defmacro deferred
   "Loads and runs a function dynamically to defer loading the namespace.
    Usage: \"(deferred clojure.core/+ 1 2 3)\" returns 6.  There's no issue
    calling require multiple times on an ns."
   [fully-qualified-func & args]
   (let [func (symbol (name fully-qualified-func))
         space (symbol (namespace fully-qualified-func))]
     `(do (require '~space)
          (let [v# (ns-resolve '~space '~func)]
            (v# ~@args)))))