My teacher taught me to do spicatto with 3 oct. G major scale, but right now i'm playing Mendelssohn's Violin concerto (3rd movement) and it's okay except for two sections with spicatto that should be played at 160 bpm (quarter notes). Anyone have tips on playing spicatto at that speed?

Spiccato has a natural frequency. To make it higher you play nearer the point of the bow and nearer the bridge on the string. That's the easy bit. Getting the fingers with the bow is what needs the practice.