Will 0,5 ml filler in each cheek really last as long as manufacturer tested it?

First of all thank you for your Question. The duration of a filler is depending on a lot of factors. The process of degradation starts right after injection, just the Speed differes from filler to filler due to its specific characteristics. One of the factors is the amount of material placed in one space. I assume that only 0,5ml of a dermal filler will give a full effect for the whole time but the effect will diminish over time and therefore the result will be seen less and less. 
Anyway, If you are not happy with the results, do not hesitate to contact your PC to have a close examination of the injected area.