Thanks @ExtraLifeMatt, did not think about that. Unfortunately it did not do it. Still 16 Bytes for FVector_NetQantize100.
bool returnValue;
TArray<uint8> binary;
FMemoryWriter writer = FMemoryWriter(binary);
FVector vector(100.f);
writer << vector;
UE_LOG(LogTemp, Error, TEXT("SizeOfVector: %d Bytes"), binary.Num());
TArray<uint8> binary2;
FMemoryWriter writer2 = FMemoryWriter(binary2);
FVector_NetQuantize100 vector100 = FVector_NetQuantize100(FVector(100.f));
vector100.NetSerialize(writer2, nullptr, returnValue);
UE_LOG(LogTemp, Error, TEXT("SizeOfNetQuantize100: %d Bytes"), binary2.Num());