other than custom pistons i dont see ant way to reach 15:1, i know cp do custom pistons, the only other way is to skim the block and re-machine the 14:1 cp pistons but i dont really want to do that, what did you have in mind to reach 16:1 without skimming the head?
You can use custom pistons and make it easy, but regardless, you should never shave a head, it just weakens it and when the tolerances drift over time you'll end up with valve issues.
To my earlier point, which you can ignore or not. The problem with this bike is in the gearbox. The engine will always be very peaky, because it has a big bore, the challenge is to get it up in the top of the revs and make it stay there.
You want to do something interesting with a crankshaft, destroke it. But it doesn't sound like you have access to the electronics to take advantage of that, unless I'm mistaken?