whats with the speed of after effects?

Hi, Im relatively new to after effects however I have read through and watched quite a few tutorials just so that I have a basic understanding. The problem is as many people complain about - the speed. I have been working with two layers, one video and one still image. My composition is 15 seconds. I have one effect on the still image. Thats it, nothing complex in any way, yet when I play it back, its all jumpy and really slow and starts and stops etc. I have changed the skip and resolution settings to try and make it a bit better but its still painfully slow.
Is this normal? If so I don't understand how does anyone actually get anything done at all. If I have to wait this long for one pissy little clip how the hell do I ever do an entire music video , ad, or film??? It doesn't make sense. Surely people need to be able to see what they are doing as they work on it?? What am I doing wrong because Im close to giving up as its getting really boring. Thanks.