It depends on your configuration.

As I know Odoo doesn't have limitations. If you are behind nginx or Apache you have to set it there.

What Birol Saglicak is saying is that there is a limit for the upload of files into the binary fields, the limit is 25 mb, not 15 mb, and it's harcoded into the js field widget as:

this.max_upload_size = 25 * 1024 * 1024; // 25Mo

If you wanna change it you have 2 ways, manually change that value in the js file at: /openerp/addons/web/static/src/js/views/form_widgets.js (line 1137 in my Odoo Community copy)

or you could load a js extension of the widgets FieldBinaryFile and FieldBinaryImage in your custom module to change that since you will not be able to get access to the widget FieldBinary where it's defined using an extension and the you need to change all the widgets that extends from FieldBinary , like:

var core = require('web.core');
var FieldBinaryFile = core.form_widget_registry.get('binary');
var FieldBinaryImage = core.form_widget_registry.get('image');
FieldBinaryFile.include({
    init: function(field_manager, node) {
        this._super(field_manager, node);
        this.max_upload_size = 50 * 1024 * 1024; // 50Mo
    }
});
FieldBinaryImage.include({
    init: function(field_manager, node) {
        this._super(field_manager, node);
        this.max_upload_size = 50 * 1024 * 1024; // 50Mo
    }
});