Hello @mrr 
Maybe first check if the problem is really the Wi-Fi. Since you have 2 devices in your local network, maybe try this:
pamac install iperf3
apt install iperf3
Start a server on one computer: iperf3 --server
Run a speed test on the second computer: iperf3 --client 192.xxx.xxx.xxx
That is a raw bandwidth test. Keep sure port 5201 is open on the server.
Also please check the availabe bandwidth:
iw dev <device> link
<device> could be wlp2s0. Check ip a.