I take my lunch insulin during or after just because of the job I have. It's better to have it on board but better to take so do what's best at the time.

I agree with SmGodwin. It depends on which insulin you are taking. Your Dr. or Diabetes Educator should have set that up with you before you started taking insulin.
If you are taking Regular and NPH. Regular you take 1/2 before you eat. NPH is a long acting so if you take that, you should have been told to take it in either the morning or bedtime or as I do both.
If you take the very quick acting insulin NOVOLOG or HUMALOG usually you count up the carbohydrates you ate and take after you eat.
I hope that kind of helps you.

I have to take my Humalog 15 minutes before I eat.

Depends on the type of insulin and your instructions from your doctor or pharmacist. They are knowledgeable.