The stock charger works great for me and I believe it's the same 18W that came with my 2XL and 3a xl. Not sure why it's taking so long but the problem is either one or the other.
Maybe it might be the charging cable. I use a power delivery cable. A regular cable that came with a fast travel charger may charge it slower. Use the pixel or purchase an Anker 18w charger and pair it with the Anker power line cable and hopefully that will help.