Something that can help a great deal is if you reduce resolution for unnecessarily large texture sizes - 4K x 4K textures are common, and each and every map (color, bump, specular, transparency) requires the full color depth with no compression be loaded into memory at the start of the render.  For 5 characters and associated clothing, this is a whole lot of memory.  A 4K x 4K map requires 16M x 24 bits (24bit color) = 48MB of memory, while a 1K x 1K map requires 1M x 24 bits = 8MB memory.

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