For such a clearance I recommend to use OP DES. If unable to meet the target V/S with THR IDLE mode active, then it is obvious that you need speedbrakes. Use them as required.
If you use V/S and SPEED mode is unable to maintain the target speed (actual speed is greater than target with the engines at idle), then it is obvious that you need speedbrakes. Physically you are doing the same, an idle descent with speedbrakes, but it is more intuitive and less confusing with the OP DES, in my opinion.
V/S is a great, great tool, however, that you can use in many situations. It allows you to tactically set the rate at which you change airplane speed. OP DES, DES, OP CLB and CLB modes include algorithms for acceleration and deceleration that depend on several factors. Sometimes they are not convenient for your particular situation and you can change that by using V/S mode. Also, V/S mode allows you a more direct control of your pitch attitude. It is like an indirect way of pulling or pushing the sidestick, so to speak. It is very useful when you have TCAS TA, to prevent a TCAS RA, for instance. If ALT* happens and you still want to use V/S because of that push to level off, then adjust the V/S.
Again, many pilots seem to be scared of using it. That is wrong. V/S is your friend, and it comes with a very good friend of its own: SPEED. And it has protections for excessive rates. What else could one ask for???
Don't forget that V/S is the pitch basic mode of the AP/FD and you must know how to use it. There are some things you have to bear in mind when using it, but nothing complicated.