It is very uncomfortable for me to carry 2000ml inside of me so I have been using 1500 and seem to get a bigger fluid output with it. Is it dangerous to switch the fluid amounts.

It may make a difference in the amount of clearance you get. Talk with your nurse and nephrologist. They should be doing a test at least every 4 months to ensure you are being adequately dialyzed. This test will determine if the 1500 mls is doing enough dialysis for you.