Textures are crucial. Keep in mind that even your textures are in JPG, PNG or other compressed format, they need to be fully decompressed to be used in 3D renderer. It means their memory footprint will significantly raise up. For example 4k texture (4096x4096) has in JPG format around 4MB – but decompressed one needs around 90MB of memory. With many textures you can easily hit memory limits – especially on mobile devices.
Because of that, we generally recommend to stay up to 4x 4k (4096x4096) textures if you are not using skybox (pano image) as a background, or 3x 4k textures plus skybox.
It gives you the best compatibility/quality ratio and quarantees your scenes will be accessible even on older mobile devices.
Of course if you dont want to support mobile devices, you can go much higher with the texture resolution.
There is also a viewer parameter that forbid access from mobile devices and display a friendly message to open it on desktop instead.