Those shafts shouldn't be too stiff for your bow, unless perhaps it's a self bow. How do you get 315 grains up front? Are you using woody weights? Are you sure your bow is cut to center and not proud of center? Even if cut to center, a thick piece of velcro for a strike plate will move the arrow out quite far, having the effect of stiffening the dynamic spine.
Are you hearing any noise like the arrow bouncing off the bow? That could be an indication of an overly soft spine, and/or brace height that's too low, which would send the arrow to the left. Of course, a too stiff spine can also bounce off the side plate and go to the left, for a right-handed shooter. Plucking can also send the arrow in that direction.
Could be lots of things. You'll just have to keep working at it to try to sort it out. Good luck.