How many reps for 15 pound weights?

Friend advised me: "Light weights, more reps. Heavy Weights, less reps" I lost my gym membership and only have 10's and 5's weights at the house..I taped them together with duct tape and i'm assuming this makes them 15's? How many reps should I do daily for this low weight? I am 18, high metabolism so i'm kinda skinny 148 lbs 5'9 thanks for any help