Best would possibly be to let all of his textures be resized by some online image editor ( or do it yourself of course ) results are that there will a bit less detail in your textures but it would reduce the mapsize by 2 times without a problem.
Ever since i started editing FTemple map i also used new textures , what i did was completely caulk my map ( Select all brushes with pushing I ) and then new textures , my map became 700 kb's down from 3500kb's and it looks a lot better now as well :p.
