For water bath canning tomato juice, the times for safety would be 35 mins pints, 40 mins qts...that's including the addition of lemon juice or citric acid for pH control and if you want to be sure there is no chance of botulism. 15 mins would be seriously under-processed, but of course, that is certainly up to you.
http://nchfp.uga.edu/how/can_03/tomato_juice.html