This is a personal choice. So you have to dig a bit deeper into what you want to do.

If you think you will like turbines, you have field access etc and will fly a lot, you will want to get the Falcon (Navy Cat really) first and then also get the F-15. The Falcon will always be great to have.....more low stress fun. It helps to get the cobwebs off your thumbs in spring. It is great to use for a first flight at a new field, etc. If you go to Jet Rallys you will want a backup plane.

If you are only going to get one plane and you know you will end up with just the F-15 and not keep both, then skip the Falcon and just get the F-15. If they are set up right that are about as easy to fly scale jet as there can be. Only negatives I have seen is the not so great ground handling with narrow mains. And some of them have a yaw waggle that is ugly but does not affect the performance.

oh and that bifurcated pipe....ugh