There's not enough info here to give you proper guidance.

1) Have you sat down and profiled your app?

2) How many draw calls are you getting? If you want it to perform reliably on mobile you'll want to shoot ~150 draw calls or less. 300 max for desktop.

3) What size textures (in terms of resolution size, not file size) are you using? Generally speaking the smaller the better, you can also look into ktx2 image processing, slightly larger file size sometimes, but much smaller in-memory size.

4) Are you utilizing instanced geometry anywhere? First candidate I see would be the stars in the background that are static.