Hello Maren!
Your dealing with a lot of 'potentials' with a tumor that large. Harsh realities with a 3.5 cm and above AN often include some of the losses you mention. You may or may not have further complication. My feeling is the remaining hearing will disappear if it's only 15% now but then, I'm not qualified to predict.
Though JHH is an excellent facility; If this were my situation I would want another opinion and that by House Ear Institute in Los Angeles ( I see Joef posted the link. ). If they just receive copy of your MRI, they will telephone an opinion.
You're pretty young to have an AN tumor at all, especially this large and I can imagine this will be a life altering event for you with much future challenge.
I don't wish to frighten you, but that you might know the potential seriousness of the situation and that HEI does more surgeries with success, and has more experience with wide varieties of situations, than any facility in the USA.
In ensuing years, please do pay very close attention to the other ear and promptly report any slight variation in hearing, tinnitus, or increased sense of being off balance. Maybe ask the Drs about NF-2 potentials as you are meeting one of the diagnostic criteria for it at being under 30 years with AN.
Best wishes and stay positive, Maren! You'll need fortitude.
Russ