There isn't one answer here — it depends on what you're doing with it.
The Levo SL2 sits in the "light eMTB" category, and Specialized ships it with a 65° head angle. That's trail-orientated: confident enough at speed on moderate terrain, but not a full enduro flop. It suits the bike's character well given it weighs significantly less than a full-power eMTB and rewards a more active riding style.
If you're mostly on flowy singletrack and want a bit more precision, the stock angle is fine as-is. If you're running steeper, rougher descents regularly, a headset cup like the Vorsprung Corset or a similar angleset to slacken it 0.5-1° gives you noticeably more confidence without turning it into a barge on the climbs.
Slacker than 64° on an SL2 starts to feel like you're fighting the bike's natural agility. It's not a Stumpjumper EVO. Work with what it is rather than trying to make it something it isn't.