24 frames per second hand-drawn animation? Have you considered reducing frame rates? Even cinema quality animation in cinemas is rarely found at only 24 frames per second. Even lowering it to 18 frames per second will save you 25% of your data.
In any case, you did not indicate where the loading time was long. Is loading from hard disk into memory a problem, or is it memory for texture loading, what is the problem? Do you often change texture datasets into the GPU, or do you just create a bunch of textures from it at boot time?
If this is a problem with disk loading, then the only real choice is to compress the texture data on the disk and unpack it into memory. S3TC compression is not compressed; It is designed to use hardware texturing compression technology. You can usually reduce it using a standard compression library like zlib, bzip2 or 7z. Of course, this means that you need to unzip it, but processors become faster than hard drives, so this is usually a gain.
If the problem is the throughput of loading the texture, then there are not many solutions for this. Well, depending on your equipment. If your hardware supports OpenCL, you can always transfer the compressed data to the GPU, and then use the OpenCL program to unzip it on the fly directly to the GPU memory. But OpenCL support will affect the minimum level of hardware that you can support.
Don't move 2D skeletal animation so fast. Games such as Odin Sphere are capable of achieving better animation of 2D skeletons, having several options for each arm position. The one that is painted, the one that matches the closest to the part of the body to which it is attached. They also use smart art to hide any defects, such as flared clothes, etc.