Wanna get 6pack for summer - how important are dieting, cardio and ab-excercises

Hello,

I've been working out for four years now and I want to get ripped now.
My current strength and physical data:

Bodyweight: 87kg
Height: 185cm
Bodyfat: ~15%

Squat: 90kg - 3x8-10
Romanian Deadlift: 100kg - 3x8-10
Dumbbell Press: 30kg - 3x8-10
Seated Cable Row: 70kg - 3x8-10
Dumbbell Shoulder Press: 20kg - 3x8-10

First of all, I've got to say that bodybuilding is my HOBBY and nothing more (I don't want to become the strongest or biggest man on earth - I want to stay healthy and look athletic). I go to the gym three times a week and perform a push-pull workout routine or rather switch to a whole-body-workout to gain strength and to give my muscles a different stimulus. I never had and probably never will have a completely defined nutrition schedule, but I know how much calories and protein I consume (normaly about 2800-3200 calories and 150-200g protein). Don't get me wrong here, but I love to eat well-balanced meals, but I also love to eat pizza, hamburgers and so on. I don't eat much junkfood, but I also don't mind to eat a cheeseburger when I feel to do so. I've never done cardio before since I'm working out (I played soccer years before), because I hate  jogging - it's so boring!

Now to come to my question:
How can I get a sixpack without a diet or rather without changing my eating habits too much? Should I do cardio and extra ab-workouts? I usually don't do extra ab-exercises, because I think that compound exercises like squats and deadlifts are enough to get strong abs. But I'm asking you to get some advices. What would be better for me? Adding two to three cardio sessions/week or would it be more effective to add a fourth workout in the gym?

Let me put it this way, you wont get 6-pack with only working out with 15% fat percent. Of course it burns calories and can make your abs bigger. You need to lose weight which is done by changing nutrition, starting more cardio or both. Change in nutrition means when you think you're eating too much but if your weight now stays the same meaning you're eating your TDEE(Daily calories needed to maintain current weight) and more cardio would do the trick alone or changing something in your nutrition. Tho you'd get the best results by doing both. I myself do not watch what I eat accurately as I don't find it always necessary. Tho I'm constantly thinking what I'm eating.

http://scoobysworkshop.com/calorie-calculator/

Cardio can be anything which rises your heart rate and keeps it there(Soccer is pretty great as it has HIIT effects):

What is good cardio?

Cardio wont interfere with your workouts if you wont overdo it.

Your routine is pretty basic. Everyone has ab muscles so no extra ab-work is not necessary but if you want you can do something for em. Hanging leg raises for example great ab exercise. 2 or 3 cardio sessions would be what I approve.

I do cardio workout days and the rest days. Doesn't really matter, one thing tho: If you do cardio after workouts your rest days will be rest days without anything. 0,5-1h cardio sessions, soccer, tennis, jogging, anything will do.