Cadence drills 220 -230spm

I'm following Coach Jeff's 5k plan. I've been doing weekly (very diffficult) cadence drills of 220 - 230spm x 4 for 30seconds. I've never been able to fully achieve this and have been waiting for it to change. How long will this continue for? 

Is anyone else struggling to achieve this or am I the only unfit one!?