between 25 and 30 I think.
I can't remember but quick question, what level is your character? cause 15 of... any stats seems rather low for getting to the place where the strength test with Roushk even happens.
something else to try is getting gear to boost strength and potion's of strength. they could make the difference.
also if your ok with using the cheat menu you can slowly raise your strength with strength cookies to find out much you need exactly then use burnt cookies to return to your old stats so you didn't actually cheat. or you can just actually cheat and make your strength like 300.
and I'm actually curious now so I'm gonna cheat cookies until I find out lol.