Ok if he makes $25,000 in sales + $1,500 minimum salary=
20% of $25,000= $5,000
if his minimum salary is $1,500 it would be $6,500 but it says or..... so he will either make $6,500 or if it's just based on his commissions, it's $5,000 If it's saying least $1,500 or greater, I'd say $5,000. If it's including his base, it's $6,500.
Hope it helps :)