The 12-14 Pro phones have had very minimal feature improvements comparatively, so we don't know if we should expect even more minimal updates to the 15 or potentially a more impressive revision to the phone overall. Time is the only answer and the 15 will most likely not be announced/released until later this fall.

If you want to wait until then, that's up to you. We're over 1/2 a year into the 14 life cycle and there are some pretty good deals for it at this point if you want to get it.