If you say two and a half hours then fine.
But that will be at a constant 746 KB/s if it stays the same all of the time while downloading.
Like I said though check what the usage policy is of the 3G adapter first.
And the data download limit per month ect.
I`m not saying it is the case but you could end up with a big bill or it could work out expensive so do check the usage allowance or data download policy before you go ahead.
The max speed of 3G is about 7.2Mb/s.
But as always it depends on how close you are to a cell tower, signal strength.
And times of the day and night, when the network may be congested.
So yes 746KB/s is quiet poor.