Sumifs Function

Hey Im not sure if im using the right function or if im using it right. I have a spreadsheet with fours sheets. I need to calculate the commision for each person on the marketing staff sheet at 15% for each campaign they are associated with on the campagin sheet and them take the 15% from the campaign charges sheet and add them all together.

Im totally lost and wondering if you could help. I think imn using the right function but could be totally lost.

Thanks.

attached is the sheet im using