Why not preselect your random celebrities, one per round?
import random
celebs = [
"a", "b", "c", "d", "e", "f",
"g", "h", "i", "j", "k", "l",
"m", "n", "o", "p", "q", "r" # need at least 15
]
chosen = random.sample(celebs, 15)
for round,celeb in enumerate(chosen, 1):
print("{}: {}".format(round, celeb))
which gives
1: j
2: a
3: r
4: f
5: n
6: o
7: g
8: k
9: i
10: l
11: e
12: b
13: d
14: q
15: p
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