A person that is not slow, might be fast. Not slow means that a person does not move at a really slow pace. It means that they move at a moderate pace or above.
It is possible to run at a slow place.
A slow pace of running
pause
pace actually means the rhythm of the poem
to walk at a slow pace
slow
slow taffy
to walk at a slow pace
4645
A pace for someone would vary from person to person, but you should probably have a slow pace.
Andante is a musical term used to mean "at a moderately slow pace", usually approximated to "walking pace".