Is it the kind that converts the interest rate into capital every month? If so, you can get it in five months.

3500000 x x 1+ 15‰)x( 1+ 15‰)x( 1+ 15‰)x( 1+ 15‰)= 3 770 494.0 13 599

Then the interest is 3 770 494.013 595-3 500 000 = 270 494.438+03 595.

If the monthly interest is not included in the principal, the interest is

3 500 000 x 0.0 15 x 5 = 262 500