I have one concern with her semblance: to be able to increase the weight of something up to 5 times the amount isn't too big of a deal. My concern falls into the fact that she can increase another person's weight up to 5 times. This is a bit too OP in that all she would have to do is simply touch someone and they are completely incapacitated, allowing her to auto-hit them with ease. I'm alright with her being able to increase her own weight, but you will have to change the ability to increase someone else's weight as that is too OP. I would suggest you get rid of that part of her ability altogether in that she is only a first year student, but make it so that she can do that once she's progressed further in Beacon and in age.
15% would be allowable for me.
I reread your character's semblance and I think we had a miscommunication somewhere: I am perfectly fine with your character being able to increase the weight of an object four or even five-fold. However, the object cannot be a living being. For a living being, increasing their weight can only be limited to a small percentage of their weight.
If you want to keep it simple, I would be perfectly fine with you being able to increase her own weight by 100% (double her weight) and 50% to anything else, whether it be a living creature or non-living. The way you have it now, 15% would actually be a bit too little for an increase. Would that work for you?