From what you describe, your kilt is probably at the right length now. A traditional kilt should be worn well above the hips - (well above where men tend to wear trousers these days.) I'm exactly the same height as you and a couple of my kilts are 25" from waist band to selvedge (hem). They rise to just under the ribcage. Also a kilt that is too short might look strange if worn with a formal type jacket or waistcoat. IMHO making this kilt shorter would be a mistake.