We are a non-profit organization raising monies for charity. We are in the process of receiving our 501(c)3. We run two raffles and a silent auction during a year. Do we need to have 15 members on our board? And would we be required to purchase a gambling license ?

The number of members on your board should be specified in your by-laws. Charitable gaming such as a raffle or Bingo night may have to be licensed by the state - rules vary so it depends on what state this is in. Auctions don't typically require any sort of license, but you will need to pay the applicable sales tax to the state on items you sell.