Adding a title page without bloating file or using fancy apps?

Just started using Zoom Pro for our small, rural municipality that does not yet have access to broadband.   Am planning to post them to YouTube - not difficult to do thanks to the modest size of the Zoom meeting files.  (GoToMeeting files for 2-3 hour meetings were easily in the 3-4GB range; a 2+ hour meeting the other night resulted in a file only 500MB).

But I wanted to add a simple title page showing date and name of the committee.  Imported file into iMovie; added a 1 second title and voila -- I ended with a 19GB file.  I may have been doing something massively wrong - I'm not an iMovie expert - but if I did, it's not obvious to me and in all events, I'm thinking there has to be a simpler way to do this without bloating the file or requiring me to buy some fancy video editing software.  I poked around in the Zoom FAQ, help and community pages, as well as online and on YouTube without success.  Anyone have suggestions?