There is no ATP check at warehouse level.
And it is certainly not a good idea to make something available that is currently moved.
This can create a lot of confusion.
The worker would get a TO to pick 15. When he arrives at the bin he can only see 10. He has no info that the other 5 will arrive in the next minutes, so he will not wait, he will pick 10 and while confirming the TO a difference of 5 will be posted.
You should evaluate cross docking functionality, why moving the 5 at all to this bin if you need them somewhere else?