Firewall or equipment that adds (symmetrical) internet speeds

Dear Sir,

We are looking for a Firewall or equipment that adds the (symmetrical) internet speeds by bringing out the total in the network for example, it accommodates two different internet connections: A (speed: 15MBS) and B (speed: 10MBS). So it will allow me to get 25MBS output in my network. Is it possible with the Fortinet? Do you know of any equipment for this purpose? Thanks for your help