inceptionv3 itsemf doesn’t have the requires_grad attribute, which is an attribute for tensors.
Setting it to False will just create a new attribute without any effect.
If you want to run inference only, you should wrap the code in a with torch.no_grad() block:
with torch.no_grad():
    out = inceptionv3(batch)

This will save some memory by avoiding to store the intermediate activations, which would be needed for the backward pass.
Calling torch.cuda.empty_cache shouldn’t give you more memory, as it will only clear the cache, which could be reused otherwise.