The Collaborative International Dictionary of English v.0.48:

xv \xv\, adj.
   The Roman number symbolizing the value fifteen.

   Syn: fifteen, 15.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

xv
    adj 1: being one more than fourteen [syn: fifteen, 15, xv]
    n 1: the cardinal number that is the sum of fourteen and one
         [syn: fifteen, 15, XV]