While aspects may have changed, 10 years ago, GIB had this rule about overcalling 1X with 1NT:
- no singleton (or void)
- no 5 card major (but can have 5 card minor)
If 16-18 HCP, stoppers in X must be at least category 2
If 15 HCP, stoppers in X must be category 4:
Quote
0 no other value
1 Qx or Jxx (partial stop)
2 Kx or Qxx (one likely stop)
3 A, QJx or 5+ HCP in the suit
4 length + HCP in suit at least 8 (two stops)
So with an extra point it would overcall 1NT, but with just 15, it requires a better club suit.
Having decided not to overcall 1NT (agree or disagree), 1
♠ seems OK.
What does North have?
What should South bid?