The Boston Celtics’ preseason has provided a glimpse into what the team could look like in the upcoming NBA season. With new players and some familiar faces battling for minutes, a few players have stood out for their performances—either positively or negatively. Here’s a look at three Celtics who raised their stock during the preseason and three who struggled to make an impact. Celtics Who Boosted Their Stock: 1. Payton Pritchard: A Rising Contributor One of the biggest winners of the Celtics’ preseason has been Payton Pritchard.…