No guarantee, but sometimes if you are the first to sit down, as soon as the dealer opens the game, especially if the dealer is standing there waiting for players, the dealer looks friendly, the pit boss looks friendly...in a quiet voice ask the dealer "May I play for $1 [e.g. less than the posted minimum]?" Dealer will quietly ask the boss "Can he play for $1?" Boss will hem/haw a little then say yes or no. I've had this work, but mostly at tables where the minimum was higher, e.g. $5 instead of $15. Maybe $2 instead of $5. Worth a try. If boss says no, don't act insulted. Just chuckle and say "OK, just thought I'd ask." Then sit down and play at the posted minimum if you want to, or keep looking.
As I said, you have to be first at the table so that it looks like you've been playing and just got 'grandfathered in' below the posted minimum. It won't work if others are already at the table playing. And, just know that if/when you leave the table you can't get back in at the lower bet.
I cruise around looking for tables getting ready to open. Won't work if table is already in play. They can't deal you in for less than what others are playing for.
Good luck!
Candy