Network connectivity issues using Hotspot in Android 15 with VPN

When being en route or traveling around, I often use Android’s Hotspot feature to connect my notebook to the outside world.

This worked completely fine for the last years.

Since the update to Android 15 (or maybe Android 14 I cannot say for sure), connecting to the Hotspot worked but almost all websites stopped loading. Fetching emails via IMAP worked but basically everything based on HTTPS resulted in timeouts or at best in partial loads after a long time.

After a lot of searching in the net and debugging the network on my notebook, I finally found the solution: the MTU.

So I reduced the MTU from the default 1500 to a little lower value of 1440 and all of my network problems are gone when using the Hotspot.

If you are using NetworkManager, it’s easy to change the MTU in the connection edit dialog:

I didn’t find what changed in the Hotspot setup between Android 13, 14 and 15 but reducing the MTU was enough to fix it.