The completion time with the starter saves will be significantly much faster since your soldiers are practically invincible and can move infinite amount of spaces on each turn. Making it impossible to fail a mission unless you extract out of one. The only thing that would be time consuming is adjusting to the mechanics of the game. knowing what research unlocks what, and the loading times on ps4. (Unless you play it on a PS5 where the loading times are improved along with framerate)
My advice is if you want to unlock the trophy for beating it on legendary difficulty first, play on the first modded save file in the thread (Vanilla Xcom 2) which includes a starter save that has ironman mode and legendary difficulty activated. since in the WOTC playthrough, the Chosen (3 bosses) will casually ambush you on missions making them a bit longer to complete until you kill them along with other new enemies. And since there are no difficulty trophies for WOTC playthroughs, you can play it on normal where there are less enemies and aren't sponges like on legendary. And the campaign is much longer in the WOTC starter saves giving you more time to unlock any trophies.
Or you can just play any of the WOTC starter saves which are on legendary difficulty and then do iron mode on the vanilla save on normal to unlock their trophies. Iron man mode is a pain since you can't manually save.
EDIT: I started on the Vanilla XCOM2 modded save. Then went to WOTC. Would recommend that since WOTC is pretty much XCOM 2.0 with more classes, new enemies, bosses, cutscenes etc and have an activated modifier to make the campaign longer. And DONT activate the "Alien Hunters DLC" on your first playthrough if you have it. It spawns mini bosses on missions that make it tedious until you kill them permanently.