If you do something in a leisurely way, you do it slowly and calmly, with no rush. A leisurely breakfast is one you sit with; a leisurely walk is one you take because you want to, not because you must get somewhere fast. The same form can describe a thing (a leisurely afternoon) or how you do it (we walked leisurely along the river). It feels gentle and a little pleasantly old-fashioned, not slang. Though actually it is not the same as lazy: lazy often sounds like a complaint, but leisurely sounds like you chose to take your time.