I hate to kill your dreams, but I don't think it's possible to get more than 14-15 in a 140mm small frame 40 mag. The tubes you have, plus the CZC long base pad, 10 coil spring/follower are the best you can do.
With 8 shot arrays if you can't get 16, it's not much better than 10 so I suggest shooting L10 major for now.