Hi @asmaamorsi,
It should not be taking that long. I just constructed my own SILVA 138.2 classifier a few days ago w/o issue. There really is no difference between 138.1 and 138.2 other than updates to the taxonomy. So, there should be no differences in the time it takes to make the classifier.
You can simply run qiime rescript get-silva-data ... to fetch and import the taxonomy for you. See the tutorial which starts with this step here.
I would strongly suggest that you set:
-cpus-per-task=1 # or 2
-mem-per-cpu=32G # or 48G
Let us know if these recommendations work. 