Could be a few things...you could have some debris blocking the valve, the shutoffs may not be fully open, or it may be normal. Newer faucets are designed to the latest Federal regulations and that means they have lower flow than older ones. You could remove the cartridge, then momentarily turn the shutoffs back on to see if you can flush anything out...just be careful, you don't need to take another shower!
Stick a pan or something underneath and see how much you get in say 30-seconds, then double it for the amount per minute. Let us know what you get. My guess is it is a little over 1 gallon (or two quarts in 30-seconds). Don't remember for sure, but I think the standard is 1.2 gpm max on a vanity faucet.