For most of us, triathlon and multi-sport is not a profession, yet a hobby. However, most of us enjoying the thrill of beating our previous time in a given race. To do this, an athlete must concentrate on "Quality" mileage versus "Junk" mileage.
Rather than focusing on time spent per week, it is more appropriate to focus on "quality" time per week. This can be done by doing every workout with a purpose. Instead of swimming three days a week for 30 minutes at a time at the exact same speed, break the workouts up and swim one day focusing on speed, one day focusing on endurance, and the third day focusing on drills and technique.
Training with a purpose takes time - in that it involves a much more detailed workout plan. One must either hire a coach who believes in uality workouts or take a hour or two each weekend to plan the next week's training schedule.
Just because "Person A" trains 15 hours a week and "Person B" trains 9 hours a week does not mean in all cases that "Person A" will be faster.