Premiere Elements - file size after editing

I took a 90 minute long MP4 video on my Samsung Galaxy S10e. I copied it to my desktop, which shows its size as 15,951,763 KB. I opened it in Premiere Elements, trimmed a few minutes off the beginning and end, and saved it. File Explorer shows the edited version's size to be 5,788,171. The amount of time I edited out cannot account for that decrease in size. When I look at the two videos on my monitor, I don't *see* a difference in quality. Has quality been lost? What accounts for that huge change in size? Just trying to understand. And to decide if there's any need to keep the bigger file. Thanks in advance for your explanation.