I have a 15 year old scar on my upper lip from a dog bite. Is there a possibility of having it completely gone? (photo)

Scarring is one of our most common concerns as plastic surgeons, both for traumatic injuries like yours or for post operative incisional scarring. After 15 years, the scar is not going to change very much. The unfortunate fact is that once there has been an injury (including surgical incisions) there is going to be a permanent scar. Sometimes we try to hide these scars in inconspicous places like behind the hairline or behind the ear. In your case, that is not an option.  None of the preparations your mentioned are going to help at this time. The best option is probably surgical. A Board Certified Plastic Surgeon should be your first stop. The scar can not be "erased" or removed but there are methods your surgeon can use to improve the appearance of the scar, decrease the size, and help make it less conspicuous by placing it in line with normal structures and natural lines. I wish you the best of luck. 

Your lip cars are completely healed and will not improve with any maneuvers; What I would recommend is considering medical tattooing of your fully matured and healed scars to camouflage them. A consultation would be necessary with a medical tattoo expert to provide you a definitive recommendation.