Reality check: over here in Germany, the legal minimum is 24 days per year. As a developer, you wouldn't take a contract below 28 days (but you also won't be offered one). 29-30 are common. My previous company allowed an additional ~5 days of unpaid leave, which many took.
Contractors in the US generally get 0 days of paid vacation. You either work or you get paid nothing since the contracting agency only makes money if you work.
Sorry, but your 10-15 days are insane.