We're developing mobile card game.
we draw all sprites in x2 size (like the original art is drawn in 696x696 and then scaled to .5) to give our sprites some kind of "reserve" in quality.
On the other hand, "approximate download" and "memory use" grow rapidly when a new portion of art comes.
A 696x696 sprite will be treated as a 1024x1024 sprite, since a lot of graphics cards (particularly on mobile) need to work with power of 2 images (i.e. 16x16, 32x32, 64x64, 128x128, 256x256, 512x512, 1024x1024, 2048x2048) and will pad out the image to the next size up.
See this blog post here
If you reduce the sprite to 512x512, it will only take a quarter of the memory of your current images and will probably give you a better balance between quality and performance.
256x256 = 256kb
512x512 = 1MB
1024x1024 = 4MB
2048x2048 = 16MB
Assuming you're filling your screen with 15 (5x3) cards, you could reduce your memory usage from 60MB down to 15MB, which is a big saving on mobile.
Also, just wanted to say that it's nice looking art you have.