Hi,
Happily running openwrt on 2 EAP615-wall devices here, thanks! Sometimes having low signal quality on one of them though.
Looking at the pictures of the device here: https://openwrt.org/toh/tp-link/eap615-wall
It seems there are 2 connectors where one could plug an IPEX to SMA adapter and then attach an external antenna. Has anyone tried that already?