-可以. But you need to get a non-immigration visa to come back if you have no AP (not file I-485 yet).So, you need to make sure you are qualified for application for a visa (e.g. H1, H4, etc.).
因為人在國內是否會slow down呢?
-No. It is irrelevant to 排期.
I also think you worry too early for this kind of thing.