TP Link EAP115?

It's not listed in the database.

Does that mean no support for openwrt?

That's correct.

802.11n is kind of old too.

You can find 802.11ac stuff at that price point, why look at an AP that only operates on the saturated 2,4 GHz band?

And remember, any router (running openwrt) can be made into an AP..

I agree that it's a bit backward in capability, though super cheap. I'd say you would be better off by a long shot if you went up at least to the EAP225, which is supported, and has 5ghz and faster speeds (and is not quite $20 more):
EAP225

Edit: That was a renewed (refurbished?) site link, a brand new one is $60 instead of $55...