The 2015 pipe is for an .21 engine so it never can be advised with a .12. I think you are a bit confused because Novarossi is using a same name on both size of engines. So look again on the Novarossi site.....

With Novarossi there is just one rule, the higher the price the faster it is configured. Because it is your first real racer I will suggest not to take the most expensive because you will not use its maximum potential. The ISON is a lower priced engine but still a good performing one.
Steel bearing or ceramic does not matter, on paper performance wise the ceramic runs better, on the track it is hard to tell the difference.