What's with all this "Glen Davis is a 10-15 minutes player" nonsense? Glen Davis is a ZERO minutes player; the amount of minutes he plays has absolutely nothing to do with how ineffective he is.
The only difference is, you just happen to notice how badly he sucks when he plays a significant amount of time and single-handedly sinks the team. He would still suck just as bad if he only played 30 seconds, but the only difference would be that you wouldn't notice it.