if you are quite fat, then it's possible to lose weight 15kg in 4 months. If not, it's quite difficult. if you are losing fat fast, gaining muscle is a bit tough. So choose which 1 do you want first

of course cardio works. Cutting food too much is not a good idea. Better to have caloric deficit doing exercise then cutting food. If can maintain both, way better. No excuse, just do the exercise