My cyst was 25cm and I was in such horrible pain that I would have said yes to them doing anything to make it better. I hope that yours doesn't end up as bad. I would say I'd get a second opinion if I was concerned about doing surgery but to go with the surgery if they both recommend it. I'd be afraid it would torque and cause all kinds of pain and problems. Plus you don't want it to grow. Mine couldn't be removed any other way than the vertical abdominal incision -- about 8". It's no fun but better than not having it taken care of. I hope it turns out OK for you. Take care.
The cyst is quite large, and with that, it could cause issues with the ovary and risk cutting off blood flow, killing the ovary basically and risking other health issues such as gangrene etc. You could ask for a second opinion but with the size of it, and the CA125 test it sounds like the dr is concerned about it and would like to remove it ASAP.
Short answer:- u need surgery!
I too hav a 20 by 17 by 13cm cyst on right overy and am having it removed via laposcopy ask ur gyn if u can hav laposcopy surgery which is far less invasive, take care K