Do you have another repro project to share that still runs out of memory with smaller images? It's expected to see higher memory usage while using RenderDoc since it is storing shadow (CPU-side) copies of graphics resources. The memory for those graphics resources for the GPU is not counted in task manager, so it's 'invisible'.
Also just in case there is some confusion you mention that you reduce the image size to "2.5MB" which doesn't quite make sense. Even though your image is stored as a .jpg, the disk size makes no difference and compressing it further will not change the memory usage in D3D11. The memory usage is entirely determined by the resolution, format and number of mip levels - in this case the .jpg in the example project you uploaded is 5184x3456 and it is created as uncompressed R8G8B8A8 with a full set of mipmaps. That's where the memory use comes from not the file size on disk.
btw, this might be more appropriate to move to a github issue.