The 6502 chip is made up of 4528 transistors (3510 enhancement transistors and 1018 depletion pullup transistors).
To put it into perspective, 64KB of DRAM contains 524288 transistors, as 1 bit of DRAM needs 1 transistor. The 6502 is mid-1970s technology while the 64KB DRAM is early-1980s technology.
Despite having so few transistors, the 6502 is generally viewed as twice as fast as the Z80 for the same clock speed. Two reasons explain it: