Here you Qui-Gon, I brightened up the image for you. Can you see the nacelles now? I don't think they look too big, I think it's more of the camera angle, zoomed in making the field of view smaller.
It is also definitely not being built in space because in the teaser there are men working on it without space suites on. So, unless they have also developed a way to breath in the vacuum of space, this is being built somewhere there is an atmosphere.