Hello
I have exactly the same question. 7.5m would be perfect. Unfortunately HDMI with 5m and 18Gbps comes to its limits. In any case, if the cable is passive. This is for electronic / physical reasons. There are also active cables that have a repeater in them so that the signal can travel longer distances. These may cause latency, but the signal can travel 10m or more. I have not yet found a good, passive 7.5m HDMI cable with 18Gbps, but you can't 100% rule out the possibility that it exists.
The best thing to do is to send an email directly to Digitec customer service: digitec@digitec.ch.
They will then give you a direct answer as to why this is taking so long / the supplier is having problems.