Suppose it takes x years to pay off the principal and interest:

1, simple interest calculation: 600000 *( 1+ 15. % * x）-（4-2.5）* 300000 *（ 1- 10%）* x = 0。

X is 1.9438+0905.

2. Compound interest calculation: 600,000 * (1+15. %）x-（4-2.5）* 300000 *（ 1- 10%）* x = 0。

X is 1.9438+0 year.

According to the meaning of the question, the above calculation results are accurate, and the loan with interest can be paid off in about two years.