I have installed a Cisco WLC 2125 and 15 LAP 1121G for an enterprise that has 130 users connected to the wireless network. There are many application servers on the local network and the users have problem of throughput when they download files from servers.
I think the problem is on the choice of the controller witch have one uplink 100 mbps to the network.
So I would like to know if there is a solution with this controller or I must use a WLC 4402-25 witch have two uplink gigabit ports.
Since the 2100 series controllers don't support LAG, your only option with them is to purchase additional ones and load-balance. If you're going to invest the money, however, you're right to say that you should move to 4400s.
What is your throughput % on that link? If you use wireless heavily, it wouldn't surprise me if you're hitting over 100Mbps with 15 APs, but it's good to check in case there's something else going on here.