At what age can you choose to live with your biological parents?

At age one my grandparents adopted me as my legal guardians. My biological mom had left me for child services as she had a bad drug addiction. I'm 15 now and not happy with the environment I'm living in as me and my grandma don't get along well at all. Chris, my biological mom has been clean and frequently being drug tested as she is on methadone for her recovery and currently has her four-year-old son living with her and her husband. We have been talking a lot lately and have a really close relationship now and I feel I would be happier in the long run living with my biological mom. I live in Alberta, Canada so could they do anything to prevent me from moving in with her?