To solve this expression, we can first simplify the numbers raised to powers:

2×5^22 = 2 x 25^11

9×5^21 = 9 x 25^10

Now we substitute these values back into the expression:

(2 x 25^11 - 9 x 25^10) / 25^15

Since all the terms are in terms of 25 raised to various powers, we can simplify:

(2 x 25^11 - 9 x 25^10) / 25^15 = (2 - 9/25) / 25^4

Now simplify further:

= (2 - 0.36) / 25^4

= (1.64) / 390625

= 0.0000041951

Therefore, the solution to the expression is 0.0000041951.