My objective of learning game development is to make a 3d relatively high graphics mobile game but that should be in 150 mb. I don't know should I start with unity or unreal engine. I found that people say unreal engine is better for 3d games and unity is better for mobile game development. As I have no experience, can anyone suggest me an engine with some reasons?
If your making a mobile game that has to fit into 150 MB you probably won't be able to show the full graphics capabilities of any of those engines. As your objective is learning I would suggest you go with Unity as its much easier to get started and to find proper resources you will need for your game. Besides better* resources, Unity will be easier to learn.