Insertion loss is just the loss when you insert e.g. a cable or a filter. So in your case yes.
S12 gives you the (frequency dependent) loss (usually in dB), S11 tells you something about the reflected energy which in turn depends on the impedance iof the cable and the connectors.
Also, make sure you are using good 50 ohm connectors or otherwise most of the losses/reflections will come from the connections between the VNA and the cable.