Which saves data?

First, i want to explain that i am a novice programmer. Like only two months in with very little knowledge prior. Ibam really just doing this to pass the time in retirement. That said, i apologize if i use terms incorrectly or if this question is answered elsewhere bit i couldnt find it with the limited terms i recogize.

Basically, i want to know which would be better - and how much better it’d be – to instantiate a prefab city at start of game or to use one of the procedural city generators and instantiate other objects onto that?

The problem im having with the city generator is that i would like to also include some buildings that are explorable, some bridges and tunnels(to serve as change scene triggers for different levels), as well as have a highway cut through and/or encircle the city. I havent found a generator that can do this (any of them, or all). If there is one, please point me to it. Otherwise, please give me tips on what id need to do to keep the size low as id hope for the game to be on mobile. (No real big plans or ideas yet, just a hobbyist with a goal).

Thank you.

Ps. Please dont waste more time than nec, a simple point in the right direction will suffice. I dont mind sifting through information to find what i want- just need to know im lookong in the right place.

Additionally, and I apologize again for the misclassification, but it deals with this still open issue…is it possible to first instantiate the bridges, tunnels and highway then generate the city around it?