J.T. Miller’s audition with the Rangers is just about in its final act. Within the next couple of days, coach John Tortorella and general manager Glen Sather are going to have to make a decision on whether the 19-year-old center gets the role as an integral part of a team with Stanley Cup aspirations, or if he is best served learning in the minors. If Miller dresses for the Rangers (7-5-0) tonight against the Islanders (4-7-1) at the Garden, it will be his fifth career NHL game. If he plays one more — the next game being Sunday at home against the Capitals — then the first year of Miller’s entry-level contract will go in effect during this lockout-shortened, 48-game season. That also would mean an accelerated timetable in terms of games played before the arrival of his restricted free agency, then just two more seasons away. “We think he’s going to be a really good player,” Tortorella said after yesterday’s optional practice. “We’re just not sure how quickly it’s going to come. So that’s our situation as an organization, to watch that.” Watch they have. In Miller’s first four games, he has spent more time impressing than disappointing, most especially in his first game on Garden ice last Thursday, a 4-1 win over the Islanders. Then, he scored his first two NHL goals and looked entirely at home with the Broadway spotlight in his face and the Broadway Hat atop his head. But it has not been all roses for the team’s 2011 first-round pick (15th overall), as Tuesday night’s 4-3 shootout win against the Bruins in Boston was probably his weakest performance in a Rangers’ uniform, and he knew it. “I’m going to need to try and stay simple,” he said one day after playing 12:24 and not registering a shot on goal at the harsh TD Garden. “I’m trying to play my game and not do too much.” Tortorella also is trying to keep an open mind about the kid from East Palestine, Ohio, who was a star for Team USA in their gold-medal performance at last month’s World Junior Championships, as well as being the youngest player named to the AHL All-Star team.