Hello,
I just strictly followed this tutorial to setup a custom OSM server : https://switch2osm.org/manually-building-a-tile-server-18-04-lts/
I did nothing more, nothing less. I imported only Belgium country.
I made a small test page with Leaflet Javascript, you can see it at this page : http://195.154.31.16/test.html
(You should scroll further to see the “slow generation” because the first tiles on the demo are now cached)
Here is my server hardware: https://www.online.net/en/server-dedicated/pro-4-l
I just installed a fresh Ubuntu 18 on it.
CPU Intel® Xeon® E5 1650 v3
RAM 96 GB DDR4 ECC
Storage 3x 500 GB SSD
Bandwidth Premium 500 Mbit/s
I will add several subdomains to parallelize calls later (tile1.server, tile2.server, tile3.server, etc…)
The tiles are generated in ~7 seconds, which is very slow in my opinion. Is this the normal behavior or did I missed something?
Thank you for you help 
Raphael