I replace my multi turn toilet shutoff valve with a 1/4 turn shutoff valve, now the water flow is much slower is there a difference in the amount of water that flows through the 1/4 turn valve
It depends on the make and model of the valve. If you look at the size of the water passage (sometimes referred to as the "port") you will get an idea of the size of the restriction. I have found that cheap imported 1/4 turn stop valves frequently have a small port. Whereas higher quality valves (more $$) may have a larger port or may even be "full port".