I don't know the xbox very well but your GPU is a custom one with a benchmark score of around 4 Teraflops. For comparison in the PC world an RTX 3060 which would be the lower end recommended for Trainz has a benchmark score of 12.7 Tflops. It could be the route is designed for an XBOX series...
A lot of content is end user created, some is more efficient than others. Try Middleton for Laptops, you can pick up most content here https://www.jatws.org/johnw/middleton.7z but you will need a couple of things from the DLS. If this one runs OK then you just need to choose you content...
So on the second computer create the data folder on the external drive going through all the steps. Assuming you're running the same version of trainz overwrite this folder with the contents of the first local data folder. Then you should be good to go. The other technique is to create .cdps...
You pays your money and takes your choice, would the 16 gigs of memory cache the memory better than having a better PCIe throughput to load the memory. I personally don't think you'll see much practical difference. At this level of GPU and trainz it's unlikely you'll max the GPU unless you...
My images are hosted on jatws.org which is based in Canada and I think they are visible to UK viewers. This UK law seems very uneven to me. I've seen nothing to indicate that I should check a person's IP address and if it is a UK one ask them to prove their age before displaying any images...