If it's running VAAI (hardware accelleration), the cloning operations will be offloaded to the storage array, which should be fast. But it does give the array more to do, which might explain the jump in load.
Maybe in your scenario you are better off disabling VAAI. You can do this on one test host to check if this helps. Have a look here for disabling VAAI: https://kb.vmware.com/s/article/1033665
I'm not sure if limiting the IOPS on a disk will also limit the IOPS during cloning, to my knowledge this won't be limited.