IKMC 2027 - Grades 7-8 - Self-study SET 2 - Thematic Batch 3 Question 21

Every asterisk in $2*0*1*5*2*0*1*5*2*0*1*5=0$ is replaced by either $+$ or $-$. What is the smallest possible number of asterisks replaced by $+$ so that the equality is true?