Please contact Tech Support (firstname.lastname@example.org) to progress this, it is not really an issue other users can fix—noting that this is a user-to-user forum (rather than formal vendor tech support).
In general I can say that neither the note count (4k notes) nor the hardware (2016 MacBook Air) seem problematic. I’ve only just swapped off a 2013 MacBook air and have used files with more notes then that.
The file size does seem overly large compared to what I’m used to seeing. Possible causes of file bloat are adding a lot of embedded files or images into $Text and/or using a lot of complexly-styled text (often when lasting from other sources).
Anyway, for this sort of issue tech support should be your first port of call. Given the file size, either compress it in a Zip or if still large, send an iCloud/Dropbox link or such as Support will likely need to see the file.