The soilpipe to this toilet runs slightly towards the toilet. Toilet water goes down slowly but waste stays. Do I need to raise the pipe?

Different size pipes require different pitch. Is yours a 3" or a 4" drain pipe after the flange?

First law of plumbing, "s " don't run uphill.
Second law of plumbing, "payday is Friday"
Third of plumbing, "you don't lick your fingers.

All humor aside, if the pipe slopes back toward the toilet, then it would have a tendency for things to be left behind if you get my drift. If the run of pipe is relatively short- a few feet then just getting it about 1/4" drop per foot of run or approximately a 2% grade will do. There are more finite numbers, but in a short span this will get things moving and ongoing use of the toilet should keep things moving out.

.. or chew on your fingernails...