Speed · Plain-English answer
The usual causes are a distant or overloaded server, a slow protocol setting, weak Wi-Fi, or an underlying connection problem that has nothing to do with the VPN. Test your speed with the VPN off, then on, then on a different server. Comparing those three results usually identifies the culprit quickly.
First test with the VPN disconnected to see what your line actually delivers, using /tools/speed-test/. If the baseline is already poor, the VPN is innocent and the problem is your connection or Wi-Fi. If the baseline is healthy, reconnect and test again.
A big drop on your usual server calls for the third test: a different server in the same or a nearby country. If the new server is fine, the old one was overloaded. If every server is slow, look at your device and settings.
Switch to a nearer server, and change the protocol to WireGuard if the app offers older options, since protocol choice alone can transform throughput. Restart the VPN app and the router to clear stale sessions, and try a cable or a better Wi-Fi position, because a weak wireless link multiplies every other loss.
On older computers and routers, encryption itself can bottleneck the processor. If speeds cap at the same figure on every server regardless of load, hardware is the likely ceiling.
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