It would be easier to use the older style ECU if you want to go the OEM ECU route. That take away a lot of wiring unless you are a beast at electrical wiring. The S15 uses a lot of different hardware and sensors. Calvin spoke about that a little bit using the OEM ecu with the NEMU board. If you find an S13 ECU that has the 4 signal wires for the coils, it makes it very easy. Good luck in the build.