Normal Shadow Clones can be fodderized with one hit:
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But Hiruzen's Shadow Clones have a lot more durability:
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Survived the genjutsu
Survived getting hit/stabbed
Survived the sealing process with Shiki Fujin
Here is more evidence -- the shurikens Hiruzen created with his chakra did not immediately disappear. Instead, they got cut in half as if they were real shuriken:
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This proves that Hiruzen can make clones that are virtually as strong as the original.
2nd example is of real Hiruzen, not a clone. I remember that fight. 3rd example doesn't prove anything. Naruto's clones will get knocked down and then disappear sometimes.
Edit: scratch what I said about the 2nd example. However, Naruto probably could preserve his clones if he wished to.