If your having trouble filling up a 16 players lobby ( I do all the time)
Here is a simple working method that has proven almost 100% effecient.
After you have clicked auto invite, invite crew/friends, skill matched players ect.
After the minimum players required has been met. You should notice a 1 minute countdown to the game starts and you can extend time by 30 seconds.
Ok so in order to get more players you should do this
-- once the timer goes to about 40 or 30 seconds in, quickly close the matchmaking and open it again--
What this does is it sends a fresh batch of invites out to random ppl, more of your friends, crew members and people who are already in the lobbys friends & crew members.
Also the closed then open on the matchmaking resets the inviting players back to 1 minute giving you more time to invite players.
Ive been doing this for sometime and have been asking ppl when they recive the invite to the match and consistantly this has been my method.
Try it out yourself but dont give up on the 1st try. You will slowly notice.