This has been asked a hell lot of times before. Perhaps Devs made the experience per second better because of all the petitions, but they have one important statement in this regard: they want you to take care of your digimons, so the level up button is a way to "worry" about the growth of your precious monsters.
Perhaps what @Tobito suggested is a better solution (5 would be enough, 10 is kind of excesive) to optimize the level ups. But we'll have to wait.
@Juketime or @Lucemon (even @Phantasmos if you're roaming still around here ), could any of you be kind and close this thread? Reasons stated above, asked a lot by now and in a lot of threads. Thanks.