the force awakens - Why is there a difference in the speed of explosions caused by the Death Star?

In A New Hope, when Alderaan is blown up by the Death Star, the destruction is instant and very explosive.

Similarly, in The Force Awakens,

when Starkiller Base fired on and destroyed Hosnian Prime (as well as a handful of smaller planets in the Hosnian system), the result was spectacularly explosive, even more so than the destruction of Alderaan.

Now, go back in time to Rogue One.

In it, both Jedha and Scarif are destroyed by the Death Star. However, both explosions are drawn out and less instantaneous. In fact, the destruction of Jedha is so “slow” that Jyn, Cassian, and the other main characters even have time to narrowly escape its destruction.

I might have missed it in the movie, but is there a reason in Rogue One why

Jedha and Scarif’s explosions were more drawn out?

Answer

It wasn’t at full power

The Death Star was not being used at full power. It only blew up a portion of the moon’s surface, not the entire moon.

“Target Jedha City,” he snapped. “Prepare single reactor ignition.”

Krennic concealed his resentment, calmed himself with the sounds of his breath and the tidal rush of the station reactor. This wasn’t how he’d imagined the culmination of twenty years’ work—a diminished attack, a grand moff’s power play—but it was the reality he contended with.

_{Rogue One: A Star Wars Story}

Similarly with Scarif:

Tarkin looked to the viewscreen and to Scarif: an ocean-drenched sphere of islands rich with rare metals, useful as a construction outpost and research incubator away from the Senate’s prying eyes. But Tarkin would not miss it. Over the years, too many officers had treated it as a place for unofficial retirement; a tropical paradise where they could neglect their duty in comfort. The loss of the Citadel and the planetary shield would be a pity—but no more than that.

“Single reactor ignition,” Tarkin said. “You may fire when ready.”

_{Rogue One: A Star Wars Story}

Perhaps Tarkin wanted to save the demonstration of the station’s true power for when he was in control of the station, and when he could properly impress the Emperor.