Not sure why you would want to? The SE and 6s share several parts (such as the A9 chip, RAM, storage & rear facing camera) but the SE also features some parts which are older/inferior to the ones in the 6s (such as the cellular modem, bluetooth and wifi chips which are shared with the 6). That and as mentioned above the logic boards are completely different so it would take some real Frankenphone engineering to make it work at all.