Hi, I'm a 17 year old guy, and I'm really quite weak. I'm 6 ft, 150 lbs, and I'm trying to start lifting weights so I can get stronger. Currently I cannot do a pull-up and can only do about 10 pushups. So yeah, I'm weak. I'm planning on getting a 15 lb dumbbell to use to build my arm muscle strength (I don't have access to a gym). I know 15 probably sounds light, but for me, its probably the heaviest weight that I could complete 3 sets of 10. But my question is about what weight dumbbell I should use to workout my back and leg muscles. Like if I were to do, say dumbbell rows, would the 15 lb dumbbell be fine for that too, or should I use a heavier weight for my back muscles compared to my arms? Thanks for the help.