Hosted tile layers run quickly on the web, but it takes an investment of server power, time, and storage space to build and maintain the tile cache. You need to prepare for the time and network resources that it takes to build a cache. You also need to anticipate the amount of disk space the cache will use on the hosting server.
View cache status
You can see the cache status on the My Content tab of the contents page of the portal by clicking the Manage Tiles link. Alternatively, you can see a status report in ArcGIS Server Manager by clicking the small grid icon 
next to the service name. This icon is available on any running map or image service that has a cache defined and is configured to use the cache (instead of drawing dynamically).
Build tiles strategically
By default, tiles are created for the full extent of the map. If you create tiles for a large geographic entity that is not rectangular, you can conserve time and processing resources on the hosting server by interactively defining the area of interest to cache. The Manage Map Server Cache Tiles tool allows you to digitize an area of interest polygon in ArcGIS Pro. This is how you constrain tile creation to an irregularly shaped boundary instead of creating tiles for the full extent of the map.
Build a cache for hosted tiles
You can build a cache on your tiles automatically when publishing, or build the cache manually after publishing. When you first start publishing, it is easier to build the cache automatically. Your tiles are created for you by your hosting server. You don't have to take further action other than optionally monitoring the cache progress.
As soon as you become familiar with what your caching needs are, though, Esri recommends that you build the cache manually. Caches that are automatically generated may be larger than you need. The larger the cache, the longer it takes to build and the more storage space it uses.
If you choose to build a cache manually after publishing your tile layer, you can launch the cache jobs from My Content in the portal. Display the item page for your tiles, click the Settings tab, and click the Manage Tiles button in the Tile Layer (hosted) Settings section. This displays a window allowing you to create tiles and view the status of each scale level.
Alternatively, you can create tile caches from ArcGIS Pro using geoprocessing tools in the caching toolset.