I've literally tried everything. It's a 64 bit 1.15.2 Vanilla Java server. It has 6gb ram already allocated. I'm hosting it on my computer. I've port forwarded. Done stuff with the firewall. I don't know what else to do.
The farthest he's gotten to playing on it is joining, seeing no blocks, just the sky and void, then getting kicked/timed out with a message saying something along the lines of "closed by the remote host", which I believe is me.
Please help. Also, let me know if you need any more information.