-15(3+x)=-6x-9

-45-15x=-6x-9
-45-15x+15x=-6x+-15x-9
-45=21x-9
-45=x-9
-45/9=5
x=5
is this right

No.

Watch your signs in this step:

-45-15x+15x=-6x+-15x-9

Yes, your solution is correct. When you simplified the equation step by step, you correctly found that x = 5.