Change the macro to /castsequence reset=15 Charge, Intercept
That way you will charge on the first press, Intercept on the second. If you do not press a second time within 15 seconds it will reset back to charge.
You can also introduce intervene to the macro by using:
/castsequence [harm] reset=15 Charge, Intercept; [help] Intervene
You just need to be careful that you do not spam the button in case you use both charge and intervene together.