Should i upgrade from my iPhone 12 to 15(maybe15 pro)or 16?

I used this phone for like 2 years,bought it at bh of 89,now its 78.I already have a person willing to buy it,and now im wondering which phone should i get.I have found base 15(256gb) and base 16(128gb) for the same price,which is 800€.Or should i stick to my 12 until its unusable?