Yes, PREVIEW is a Scrabble word!

Letter values in Scrabble US: P 3, R 1, E 1, V 4, I 1, E 1, W 4.

Is it a valid word?

PREVIEW is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

an advertisement consisting of short scenes from a motion picture that will appear in the near future
a screening for a select audience in advance of release for the general public