comcasa good question! Actually yes, depending on the resolution and the number of textures we need to resize this might add substantially to the loading time.
As we speak, we're optimizing this for the next release to run in parallel, so that you can navigate through your model while textures are still beeing processed.
But if you know beforehand that you don't require the textures to be in full resolution you can downscale them before hand and this will definitely speed things up either way. If you look into the log files (%AppData%\Roaming\Enscape\Data\Logs) you can actually see which textures are getting resized to what resolution.