$setViewValue with object copy performance - angularjs

Question

I have a directive for a toggle button derived from the btnRadio of Angular UI. Instead of just using a simple model with toggled values I have modified it to accept a model which is a "global" object used by all the directive instances - I pass the key to the directive in order to extract the particular data. In my directive I search through this object and handle it from there. All works great but I have a performance concern. In the directive I have to make a copy of the model (per Angular docs) and reapply that to my view using ngModelController.$setViewValue. This model can contain 100's of entries. And this directive can appear a few dozen times. Is there a potential for some memory leak if I create copies of the this large object in every directive?
Here's the directive:
app.directive('btnChoice', function () {
return {
require: ['btnChoice', 'ngModel'],
controller: 'ButtonsController',
link: function (scope, element, attrs, ctrls) {
var buttonsCtrl = ctrls[0], ngModelCtrl = ctrls[1];
function getChoice() {
var val = scope.$eval(attrs.btnValue);
console.log(val);
return (angular.isDefined(val) && ngModelCtrl.$modelValue && ngModelCtrl.$modelValue[val]) ? ngModelCtrl.$modelValue[val] : false;
}
//model -> UI
ngModelCtrl.$render = function () {
element.toggleClass(buttonsCtrl.activeClass, angular.equals(getChoice(), attrs.btnChoice));
};
//ui->model
element.bind(buttonsCtrl.toggleEvent, function () {
if (!element.hasClass(buttonsCtrl.activeClass)) {
scope.$apply(function () {
var ev = attrs.btnEvent;
var c = attrs.btnChoice;
var v = scope.$eval(attrs.btnValue);
scope.$emit(ev, { model: v, value: c });
ngModelCtrl.$modelValue[v] = c;
// The line below worries me
ngModelCtrl.$setViewValue(angular.copy(ngModelCtrl.$modelValue););
ngModelCtrl.$render();
});
}
});
}
};
});
Here's the view:
<div class="btn-group">
<label class="btn btn-primary" ng-model="$attendances" btn-event="attend" btn-choice="yes" btn-value="item.id">Yup</label>
<label class="btn btn-primary" ng-model="$attendances" btn-event="attend" btn-choice="maybe" btn-value="item.id">Maybe</label>
<label class="btn btn-primary" ng-model="$attendances" btn-event="attend" btn-choice="no" btn-value="item.id">Nope</label>
</div>
The model looks like:
var model = {
'7612tas337213': 'yes',
'7q23423h1237s': 'maybe
}