@Heilmar, of course the T1500G-8T has a »Save« button.

New web UI:

Old web UI:

Always save the config if you want to make changed settings persistent after having applied them for testing.

The only setting you don't need to save after applying is the selection of the Next Startup firmware image in the »Boot Config« menu.

Thus, IMO the »Apply« button in the »Boot Config« menu should be renamed to »Save« in the new web UI, since applying this setting requires a reboot of the switch anyway, but I mention this only for Anderson as a possible feature request.

Heilmar wrote

I have saved the config, but after the reboot I had the default ip again, even after I restored the saves config

So you think the switch has a defect? Could be, but I doubt this if the web UI is running already.

Please try again. Set factory settings first (press the RESET button for 5 to 7 seconds).
Then log in using the switch's standard IP 192.168.0.1 and change the IP to the one you want to use and apply the new setting.

As soon as you now hit »Apply« the connection from your PC/laptop to the switch will be lost.

The new web UI can not show this disconnect state as clearly as the old web UI did when navigating through menus any further.
You can even hit »Save«, but it seems that nothing will happen.

Thus, pressing »Save« does not have any effect unless you change the PC/laptop's IP, re-connect to the switch, log in again and then save the setting.

Make sure that the switch is neither powered off nor rebooted until you have saved the new setting successfully.
Then reboot again to check the new IP.