As noted by by Fergal19, you should contact your AVC broker (eg, Cornmarket) a few months before retirement about this. They will do the calculations re the maximum you can take as a tax free lump sum from the AVC fund to top up your main scheme lump sum. They should liaise with your pay/pension department about this.
I am not sure about your calculations and hope you are correct. More pessimistically, the Revenue max may be €55k*3*25/80 = €51.5k. That would leave an AVC top up of €14.5k. Hopefully this is wrong.
EDIT: On checking, this pessimistic calculation is wrong. I believe your sums are correct, czechmate.