Kyle has a third of Fabian's number of marbles, so he has 15 / 3 = <<15/3=5>>5 marbles.
Miles has a fifth of Fabian's number of marbles, so he has 15 / 5 = <<15/5=3>>3 marbles.
Miles and Kyle together have 5 + 3 = <<5+3=8>>8 marbles.
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