Can I improve the life of pH sensor when I choose 225 mm electrode in place of 120 mm electrode?

That is possible but not guaranteed. The 225 mm sensor body is longer, so it has more electrolyte. Often the reference electrode fails because the electrolyte is depleted as it diffuses through the reference junction into the process. With a higher volume of electrolye this process will take a longer time. This is not the only failure mode so you can still have a short lifetime due to another cause.