Cutting 3D dimensional surfaces take a while. No way around it, you trade time for finish quality. If you want it to take shorter it will look worse. If you must speed things up a little bit use decent CAM software, which will let you pick surfaces and optimize feed an step over to each where you need it. Not a trivial exercise, and these programs are pretty expensive. It also takes a fair amount of skill to effectively toolpath 3D surfaces.
If you get good looking results with what you have, the path to speed is going to come at a great cost. That's why people pay big bucks for fancy high speed machinery with high speed spindles, to get higher feed rates.
You may be able to increase your feeds as well. Are you roughing out with a separate operation? Using a square end mill, or a larger ball mill and step over you can get rid of material quickly, then speed up feeds for the finishing pass where you are ideally removing little material at small step overs.