Disable Pool Member and Persistence session should die??

I guess one simple way would be to kill the service on the member, ie stopping the site for a second.

Or try to delete the persistence records for the node via tmsh:

tmsh delete persist-records node-addr 10.0.0.15

To kill the connections to a specific member you can try this one:

tmsh delete /sys connection ss-server-addr 10.0.0.15 ss-server-port 80

/Patrik