Opposite a 15-17 one notrump, many players have a relatively simple guideline: insist on game with 10 HCP, invite with 9 HCP, and consider inviting with 8 HCP.
We’d like to introduce you to a guideline that we have found to be more accurate when you have a balanced hand with no five-card suit: the Rule of 16. Add (1) the number of HCP to (2) the number of cards nine and higher; if the total is 16 or more, insist on game; if the total is 15, invite game; if the total is 14, consider inviting.
Of course, if your opening 1NT range is not 15-17 you would need to make adjustments before adopting this guideline. In our partnership, the opening 1NT range is 14-16 in first and second seats, so we use a Rule of 17.