optimization of codeigniter php script to consume less memory. -- 2

I am looking for well experience and good technical skill codeigniter php coder to optimize my php script so it will load and consume memory under 32mb. previous developer migrate our codeigniter php script codes from 5.2 to 5.6. but it's not completely optimize so it's consuming lot of memory. earlier same script under php 5.2 load very well and consume memory under 32mb.