10-15 cm is a bit much on the vest ^^;; thats about 6 inches 1-2 cm or 0.5-1 inchs below the shoulder bells perhaps, I would say.
Regarding the riding patch, I guess you could glue it even, there are specialized glues for this, but I do not know how good it will hold up in the crotch area , so you might have to re-glue regulary.
Otherwise try what chef said about sewing