Is the lingering scent of yellowish discharge considered a barrier to performing ghusl after the cessation of blood and clear secretions, or must one wait another 15 days, or can one perform ghusl immediately?

The Fatwa's Conclusion:

Yellowish and brownish discharges are considered menses if they are connected to menstrual bleeding. A woman becomes pure when she sees the white discharge (al-qassah al-bayda') or experiences complete dryness. The clear white discharges you observed are among the signs of purity.