Clojure's numeric tower is useful, but it can put a lot of steps between you and simple arithmetic. Unfortunately, while Clojure will warn you when reflection is required to invoke a function, it will not warn you when reflection is required to perform math. The only reliable way to discover whether you're calling clojure.lang.Number.add(Object, Object) or clojure.lang.Number.add(long, long) is to use a profiler or decompiler.
Or you can just bypass Clojure's math operators altogether.
In the primitive-math namespace, there are equivalents for every arithmetic operator and comparator that will give a reflection warning if it cannot compile down to a simple, predictable, unboxed mathematical operation.