They hold 15% of total FOREIGN holdings.
The government in its reporting segregates out what portions of the US debt are held by foreign governments.
Approximately 25% of our total us debt is held by those classified as 'foreign'. They own 15% of that 25% sub classification.
The US has about $8.87 trillion out.
Only 25% of that counts as foreign owned.
Your number is a sub segment of the bigger picture, not the bigger picture itself.
Ok, closer to 4%.
They have been waffling in between 3-4% for years. Sometimes up, sometimes down. At this moment in time, its around 3.9%.