No, Only RAM does not determine the speed of the Laptop or the System. Also the Clock Speed matters. Clock speed is always determined in GHz(gigahertz) or MHz that determines the cycles per second, i.e., 1GHz represents 1000 Mega cycles per second that is the number of clock ticks per second. The CPU always needs a fixed number of clock cycles (clock ticks)per second to execute each instruction. The more instructions the CPU can execute per second when the clock cycles are faster.
Hence the clock speed (GHz) also required for the laptop or PC to give higher performace