It's pretty much been said... you can't increase it unless you buy another welder...

If it's a hobby welder and maybe a toy to learn some welding techniques with... realistically, when are you going to be welding for 1.5 minutes straight?
If you make a 15-20 second zap here and look at the weld, hit it with the hammer, do whatever, that whole time is rest time... another 15-20 second zap with the welder.
Very few times are you going to be welding anything that you'll weld for 1.5 minutes straight without stopping, especially if it's a stick welder... you'll have to stop to change sticks.

Unless you are doing a lot of welding or building something, I wouldn't worry about it. If you want a really good welder, start saving now. You have a unit that will do a light duty job and didn't cost a lot. If you start saving now, when you get good at welding or that one craps out on you, you'll have some money to go buy a really good name brand unit like others have suggested.