Hello Mihai,
The short answer to your question would be ‘no’. Exporting the files / sequence will read from the source material, so exporting them separately, on a timeline or nested (‘on a timeline as a timeline’) will all still refer to the original .MTS files.
If you would like to export them as 1 single file, it’d be easiest to just drag them onto a timeline and export that as a QT .mov.
What nesting would be useful for, is working with the separate MTS files as though they were 1 file without having to transcode them to h.264, or ‘flattening’ a bunch of video layers without having to pass a render on them.
If you’re sure you are transcoding to h.264, nesting will not do anything to speed up your rendertimes.