weaker how?
15lb flouro funnily enough will break at pretty much the same strain as 15lb mono...
Main things to know about mono is theres much less stretch, it tends to be much stiffer, tends to sink like a stone, will be thicker diameter for the same breaking strain vs mono, can be tougher to use mono knots (due to thickness and stiffness)
Big positives tend to be more abrasion resistant, and good refractive index. I tend to only really use it when fishing for chub/barbel in gin clear water conditions.