Yes, it is possible to determine the number of tiles in a Tile Package file (.tpk) before publishing to ArcGIS Online. This is commonly done as best practice to ensure the number of tiles are correct before publication.
- After the .tpk file is created, make a copy of the file.
- Change the extension of the copy version to .7z.
- Extract the files from the copy version using a compression software such as WinZip.
- In ArcCatalog or the Catalog pane, browse to the folder of the extracted files in Step 3.
- Navigate to folder v101, right-click the raster dataset and select Properties.
- In the Raster Dataset Properties window, select the Cache Scheme tab.
- Refer to the amount listed at the Number of Tiles: field.