No I didn't see it.
Yes I can invade it at turn 15.
The thing is I have the option to infiltrate but I can't recruit spies. This if the WT to infiltrate:
Step Four: Visit the brothel and recruit a spy. You can recruit one spy per week from the menu there.
Step Five: Visit Raeve keep. (You may need to do this twice to get to the right menu if it's your first time there.) Choose the Infiltrate option from the list of choices; in the current build, I don't think any of the spies' traits matter, so pick any you have access to.
This is what I have in the spies tab of the brothel:
View attachment 1595757
When I press infiltrate even without recruiting It changes to: "1 spy currently on other assignments". After a couple of turns it disappeared.