J.G.
I hate to say it, but you are going to have to keep the 15 month old away from the other kids if they aren't supervised. The quickest way to end pulling is by a quick removal from the situation. I put my son in his crib about 3 times, and that was that. I did the same when he started hitting.
Now, I know it is impossible to always be there. Trust me, my kids play alone all day long. I told my daughter to just quickly yell for me.
But I do think quick, fast isolation and removal is the fastest way to teach them what the "no" actually means.