Yes, REMINISCENCES is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, M 3, I 1, N 1, I 1, S 1, C 3, E 1, N 1, C 3, E 1, S 1.

Is it a valid word?

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

a mental impression retained and recalled from the past
the process of remembering (especially the process of recovering information by mental effort)