Solution - Simplification or other simple results

Step  1  :

 1.1     8 = 23

(8)² = (2³)² = 2⁶

Equation at the end of step  1  :

  (152) +  26

Step  2  :

 2.1     15 = 3•5

(15)² = (3•5)² = 3² • 5²

Equation at the end of step  2  :

  (32•52) +  26

Step  3  :

Final result :

  289