Being a vector-based application, Illustrator assumes the default pixel density of documents is 72ppi.
If you export at 150ppi, then you ask illustrator to effectively double the pixel density, but it won't. Illustrator always exports assuming 72ppi.
So, what you get when you export at 150ppi, is a document about twice the dimensions of the original - i.e. 960x2030px - and not an increase in pixel density (PPI).
Export at 300ppi and you get a document roughly 4x the original pixel dimensions.
If you need the document to remain at 480x1015px, you must export at 72ppi. Illustrator will not increase the pixel density of exports. The pixel dimensions will be increased as opposed to pixel density being increased.
You can test this yourself. Export at the various resolutions, then examine the exports. You'll find they are different dimensions not different densities (PPI).
Why can't Illustrator calculate pixel density upon export?
Well, you'd have to ask Adobe about that.
You can use a separate tool, such as Photoshop, to reduce the export file dimensions back to where you need them while increasing the pixel density (PPI). But Illustrator can't do this. - or simply place the Illustrator file as a smart object into a Photoshop document with the correct dimensions and resolution for your needs.
As for the quality, that's your call - it's a balance between the quality setting, the quality of the exported image, and the resulting file size (kb). Each image can be different and there's no universal setting, other than maximum, which works for every image.
Compression Method is best left on the default (standard) unless you know why you need to change it.
Anti-aliasing depends upon the nature of the artwork. If there's no, or minimal, type in the artwork using the Art Optimized (supersampling) setting is generally better.
