~43 megabytes all together then. Thats a lot less than 500+ so your problem must
be elswhere.

Can you try it without the sky AND ship models to get a base nexus number?

27 megabytes is probably right for the sky cube, but it is on the high side.
Are you loading the skins internally with the model? If so , is 24 bit set,
and mipmaps on or off? You might be loading the images as 32 bit. Depending on
how you use the cube, you probably can get by without mipmaps.

15 megs for the spaceship model seems extremely high for one 1024 texture.