I have just implemented another option, BC7 (ASTC still available, it's a drop down). BC7 is supported on basically all GPUs made in the last 15 years. Same visual quality as ASTC, but takes more space. Compared to uncompressed it uses 4x less VRAM (ASTC would use 9x less VRAM but no GPUs support it so VRAM tends to be unaffected) and gives the same improved load times as ASTC. However, it is larger, even more so than uncompressed images (on disk they are compressed with PNG or JPEG which are a lot more efficient but don't work for GPU random access), from my testing BC7 takes 60% more disk space than uncompressed, while ASTC takes 20% less disk space than uncompressed (used to be roughly same, but I added ZSTD compression at rest to mitigate BC7 disk usage, which made ASTC more efficient on disk too).
Still, for me this is a much better option, images load instantly and I don't care too much about the extra disk space it uses (I have 1.1gb uncompressed, 0.9gb astc and 1.8gb bc7).
For VRAM usage: after loading all images I have, nvtop showed 12gb VRAM and 2gb RAM (I think it didn't allow more into VRAM to not fill it so the extra went into RAM) when uncompressed. With BC7 I can load all images at once and it uses 4gb VRAM, and no RAM increase. But of course, I'll be using BC7 along with unload off screen, so almost no VRAM is used and loading images is faster.