There is an online Karnaugh Map solver here. If you enter your data there on the four input variable page, it comes up with 4 sum of product terms and three product of sum terms.
You get the same result from this logic minimization page, which also prints out the Karnaugh Map.
If 15 was also set, then you could have two product terms as long as you had an active low output. Remember that you can combine terms by wrapping around the ends of the map to the opposite edge.