Mainly depends on your bandwidth speed you bought and can vary as they will be connected to various other media types (computers, phones, iPad, etc.) in your house, however it can also be increased by either using a Ethernet cable to get a better connection between PS3 and the router if not close already using Wi-Fi (Not Strong Strength). Moreover, I think u can adjust the Internet settings for the Proxy server or DNS to speed up downloads.
I do not know much about changing the proxy server or DNS numbers, so I wont requesting asking me, futhermore other answers may be better instructed on how to improve this.
Hope this Helped