x^2+2x-15/4x^2/x^2-25/2x-10

You need to use parentheses to clarify the meaning of what you wrote. You can't have a four-story fraction with three / signs

x^2+2x-15 factors into (x+5)(x-3)
There is also an (x+5) factor in x^2-25,and an (x-5) factor in 2x-10.

That should lead to some cancellations