Postseason basketball is supposed to tighten spreads, not blow them open. So when a LeBron-led Lakers team opens as a 15.5-point dog in a Game 1, that's the books telling you they don't think this is a fight. They think it's a scheduled execution.
15.5 is a wild place to start a playoff series. That's not a 'home court is tough' line, that's a 'we don't think the Lakers can hang' line. LeBron at 40-plus has done a lot of impossible things, but covering 2 touchdowns against the team built to dismantle him isn't usually one of them. The market is screaming that this matchup is broken before the ball even goes up.
The interesting wrinkle is the player-prop angle. A 15.5-point spread suggests one team is getting cooked, but individual stat slices on SGA and LeBron don't really care who wins by 20. SGA is the engine of the favorite and LeBron is going to get his shots up no matter the scoreboard, so the prop market might be where the actual sweat lives tonight.
Either way, the storyline writes itself. If the Lakers cover, it's a moral win and the LeBron-defies-Vegas narrative gets another chapter. If they get bulldozed, the obituaries start getting drafted before the buzzer. Books don't usually hand out 15.5 in May for no reason.