Can i get the child tax credit for my 15 yr old dependant?

Yes, you can get the child tax credit for a 15yr old dependent if you meet all of these qualifications.  

• Be under age 17 at the end of the tax year
• Is your son, daughter, stepchild, foster child, adopted child, brother, sister, stepbrother, stepsister, half-brother, half-sister, or a descendant of any of them (for example, a grandchild, niece, or nephew)
• Has his or her own Social Security Number
  • Children with ITINs don't qualify, but may instead be eligible for the $500 Credit for Other Dependents
• Lived with you for more than half the year
• Didn't support him/herself (didn't pay more than half their own expenses)
• Is a U.S. citizen, U.S. national, or U.S. resident alien
  • Residents of Canada or Mexico wouldn't qualify

Up to $1,400 of the credit is refundable and is phased-in based on your earned income.  In most cases, you must have $2,500 or more of earned income to be eligible for any portion of the refundable Child Tax Credit.

The $2,000 per-child credit is reduced once your AGI reaches $200,000 (or $400,000 if you're filing jointly with your spouse).