(+1s should be given for least wordy question on site)
No it's not!
This is actually Nora Leonhardt who was the stand-in for Marina Sirtis who played Troi.
Here's a picture of Leonhardt:
and now compared with Sirtis:
In fact, she's not actually playing Troi in the above image; it's some junior science officer who holds the rank of ensign. If you look closely at the above picture, you'll see that that character isn't actually Deanna Troi at all - she has only got the rank of ensign; but we know that
By 2364, Troi held the rank of lieutenant commander. That year, she was assigned as ship's counselor aboard the USS Enterprise-D. (TNG: "Encounter at Farpoint")