> 3G HSPA (~1.5Mbit/s): 8 seconds

1.5Mbit/sec is the theoretical maximum output of HSPA. That means people will perceive much less then that. And 3G is something which is still used by people. My mobile phone falls back to 3G whenever there is no better broadcasting signal. Many websites become unusable with slow mobile uplink. That's a terrible state for the web.