My 15 month old has an attention span of like 2 seconds and is very mean to other kids her dad has ADHD bipolar and ptsd is the cause for concern?

No, yes, and maybe. A toddler with short attention is not a concern, but yes a toddler who's mean to others is a problem. Parents with such a child can work with a pediatrician plus learn special parenting skills to get rid of the meanness. A history of psychiatric illness is both bad and good. It's bad to have, but it's good that the illness is known, so parents can try to prevent the child from getting the illness.
Dad get help too! I would add to the wonderful response from dr kwok, that ideally the dad himself would be getting in treatment to work on his own issues (bipolar adhd & ptsd), so as not to be modeling the very behavior that you're trying to change in your kid (not to mention for his own sake!) good luck!
Not exactly. While family history of adhd means your child is at a higher risk of developing adhd than a child who doesn't have that in their background, 15 months is way to early to say they have it. Little kids simply naturally have very short attention spans, and he may still grow out of it. Talk to his pediatrician about your concerns.
Be patient. I expect an infant to have an attention span of no more than a minute per year of age. For them to move from issue to issue quickly early on does not mean they will be ADHD or anything else. Find a parenting support group so you can all share tidbits of surviving parenting.