I'd concur that conversion to DDS is likely the best bet on size savings.
You might also want to try PngGauntlet (https://pnggauntlet.com/) or similar PNG optimizers. Though I'd think the in memory size won't be reduced by such.
You might also want to try PngGauntlet (https://pnggauntlet.com/) or similar PNG optimizers. Though I'd think the in memory size won't be reduced by such.