Total bet is equal to regular bet plus side bet

At wind creek, the Kings bounty and 21+3 side bets are factored into the total bet. If the table minimum is 15 dollars I can bet 10 dollars on the regular blackjack bet and 5 on one of the side bets. Does this give me any kind of advantage or does it give the house any less of an advantage, or is this normal practice elsewhere?

If you put $15 out for blackjack, you are exposing your money to the house edge for the basic game. Let’s assume good rules for a 0.46% house edge. Let’s also assume the 21+3 side bet is the variant with the least house edge of 3.24%. If you wager $10 on blackjack and $5 on the 21+3 side bet you are exposing your $15 to a cumulative 1.39% house edge for an average loss of about $0.21 per hand.

If you had to bet $15 on blackjack to place your $5 21+3 side bet you would expose your $20 total of wagers to a cumulative house edge of 1.16% for an average loss of about $0.23 per hand.

If you are playing for entertainment and want to place the side bet you could consider wagering less at a higher house edge an advantage because the expected loss is lower. If you stick to blackjack only the expected loss per hand would be $0.07.

Every side bet is bad.

I have heard that Carnival ships' casinos have a $6 minimum on their Spanish 21 variant table. Most players bet $5 on the main bet and $1 on the side bet, but betting $6 (or more) only on the main bet is allowed.

Also, I believe Bally's Atlantic City has a similar rule on at least some of their blackjack tables.