RUT955 should definitely be able to reach higher speeds than 20Mbps. I've run a quick speed test on RUT955 with an EC25-EU modem, and with a good signal, I was able to reach a download speed of 55Mbps down and 36Mbps up, with a latency of 25ms (14860403978).
Here are the signal parameters during testing:
Looking at your troubleshoot file, it seems like you are connected to band 8, which operates in the 900MHz frequency range. This band (as well as band 20, and band 28 in the European continent) are designed to cover more area, rather than provide high throughput. Adding to that, the signal values are also quite poor, so you are either in an area with poor coverage, or antennas are not mounted properly.
Since the device is being used in a campervan, I'd recommend upgrading to an external omnidirectional antenna. Poynting is our partner who specializes in antennas and might be able to help you out.
Finally, if you are often in the same are, I'd also recommend exploring other carriers, as the coverage also highly depends on what capabilities the operator can offer.