Knowing little about the subject. If Insulin is a 20 minute lag, and eating is a 20 minute lag. Shouldn't you just dose immediately before eating so they hit at the same time?
Anyways there are studies about the "inject 15min before food" approach: eg. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2945151/
Glucose acts more in harsh peaks. So you want the glucose peak to hit when you are at the maximum of insulin action. Hence the 15mins delay.
This is all roughly speaking, YMMV.