Here, Twice fast means, she takes half time in doing same amount of work.
Let, Anna takes = 2t & Jane takes = t
It would be: 1/t + 1/2t = 1/15
2t + t / 2t² = 1/15
15(3t) = 2t²
2t² = 45t
Divide both sides by t,
2t = 45
t = 45/2
t = 22.5
& 2t = 22.5(2) = 45
In short, Anna would take 45 minutes
Hope this helps!
