It won't hurt to go up to maybe a +3 size (17") as long as you don't go crazy with rim width. Low profile tires are the first stop to improved handling and grip. Getting some offset will help avoid the inside edge of the rim fouling the upper front control arms but then you will need to factor in it either possibly fouling the fenders or the dreaded bump steer (a steering damper/stabiliser will help to tone that down).