Eatting through sparks

Hi guys, since I have changed over to my Vance and Hines Twin Slash Staggered exhaust I have found I am going through spark plugs quicker than normal. After I did all the work on it back in September the plugs have been changed three times. Some new ones got put in just before Christmas and then I found about 2 months later it failed to start and it was discovered it was due to the sparks already being burnt out (I assumed as it was colder this happened quicker). I took my bike back into the garage towards the end of May to get it all checked over before my holiday (which sadly never happened) and it turns out they were already blackening and got changed and now currently have some Iridium ones in (only ones Halfords had in). Is there a way to stop this happening?