I think Mobil 1 10w30 would do you well (or any type of synthetic 10w30), it's a bit heavier than 5w30. I don't know if I'd do the 5w30 to 15w40 jump all of a sudden, I know it's just oil, but some cars do weird things when you change types/weights of oils. And being it's a DSM and all, anything is possible.
