This is probably a dumb question from a Pennsylvanian but weren't 715T's purchased before the Safe Act grandfathered so you can keep it like it was made? Did it need to be registered to be grandfathered? Feel free to not answer those questions publicly here as you never know who is reading this.
Beyond how old the 715T is it seems rather difficult to be modified into legal status in NY. Look at the Safe Act compliant "AR-15's" for an idea of how far it needs to be altered. I suggest you proceed with caution. Just because you think it's legal or someone on the internet thinks it's legal doesn't mean a policeman or judge will.