GL-X3000 Zscaler issue

I have a number of phones / pcs laptops all running through my GL-X3000 with a EE unlimited data sim.
I am getting at least 30 meg download on all but one devices which I am happy with.

The one device causing issues is my partners work laptop. She has ZScaler installed as part of a secure network access to her work environment. Her network speed is lower than 8 meg via the GL-X3000. (wifi or direct connect)

I have not touched the VPN side of the router, but wondered if I should be changing a setting to allow better speeds when Zscaler is used, that would not affect other devices.

If Zscaler works like an VPN it’s pretty common that the speeds are slower because will be send to the company before getting to the internet

We have 15 meg Sky broadband (no fibre until 2026 according to Openreach), hence the reason for looking for a faster solution.
On 15meg, her Teams and spreadsheets are slow, but workable. Going from 30 meg on the EE sim dropping to 8, just seems excessive. Even if it dropped to 20meg, we would be better off.
She has to have the VPN (Zscaler) running. We don’t have admin access to turn it off.

Then you have to live with it, unfortunately.

Speed depends not mostly on your router but her VPN connection and upload speed. Maybe all traffic will be send by her company over VPN

Yes, I think that the VPN could be the issue. For security reasons she has to keep the VPN on.