Isn't Boost Mobile CDMA and cricket is GSM???
I'm not sure if the Iphone 6 is compatible or not, sorry.
Edit: also, I'm sure if you have any contracts with Boost that need to be fulfilled, you may not be able to unlock it, if possible, to Cricket. You may have to get the code from Boost.
It's a little confusing to me, but perhaps someone else can shed some light