Given this is a local install running in an essentially development environment rather than on a proper server which is tuned in various ways, I wouldn't worry too much at this point.
Personally, I can't produce what you're demonstrating here even in a development environment, and certainly can't in a production environment so overall I don't think there's anything too concerning here.
If it's something you wanted to try and address (either locally or if the issues persist later) you'd need to be looking at server configuration mostly in the first instance. PHP 7.x can certainly help with performance, there are various bits of tuning you can do with MySQL and of course making sure there's plenty of RAM available, and your files and DB being accessible from an SSD would all have a decent impact on performance.