To answer your question, it might've been worth a shot to throw your dusk balls at the Solgaleo.
In Pokémon Sun, Dusk Balls have a 1x catch modifier during the day. This is equivalent to a traditional PokeBall.
At your odds (with Solgaleo being at 12.5% of its HP and being paralyzed), you would've had a 34.568% chance of catching it. By using two of your available balls, you would've had a little over a 50% catch rate, as well. This is quite high, so it was probably worth trying out those Dusk Balls. .
I Hope I Helped!
Source 1 (Calculator)