No. Project64 1.7 will have a feature that lets you slow down or speed up the emulator incrementally, AFAIK.
If you think that the game is slow, and you don't get steady 60/60 or 50/50 then your system is underpowered. If you do get steady framerate but the game still feels slow, that how the game is supposed to be. Note: don't play PAL games unless you really have to.