If that’s the case, you have unmatched items / non analyzed items /etc. If you have no new items, it should be instant (assuming you have the directory structure already there and it’s not repolling that).
If I do just a find:
felix@gemini:/GD$ time find . | wc -l
25086
real 0m0.133s
user 0m0.008s
sys 0m0.012s
When cached it takes that long. The first scan/cache build for the directory/files takes 3-5 minutes.
If I scan when a new item, it uses autoscan and does it’s magic:
2018-11-08 16:22:20,070 - INFO - AUTOSCAN [140252836681472]: Client '127.0.0.1' scan request for series: '/gmedia/TV/Single.Parents/Single.Parents.S01E07.mkv', event: 'Download'
2018-11-08 16:22:20,070 - INFO - PLEX [140252769945344]: Scan request from Sonarr for '/gmedia/TV/Single.Parents/Single.Parents.S01E07.mkv', sleeping for 5 seconds...
2018-11-08 16:22:25,076 - INFO - PLEX [140252769945344]: File '/gmedia/TV/Single.Parents/Single.Parents.S01E07.mkv' exists on check 1 of 10.
2018-11-08 16:22:25,076 - INFO - PLEX [140252769945344]: Scan request is now being processed
2018-11-08 16:22:25,088 - INFO - PLEX [140252769945344]: No 'Plex Media Scanner' processes were found.
2018-11-08 16:22:25,089 - INFO - PLEX [140252769945344]: Starting Plex Scanner
2018-11-08 16:22:25,777 - INFO - UTILS [140252769945344]: GUI: Scanning Single Parents Season 1 Episode 1
2018-11-08 16:22:25,780 - INFO - UTILS [140252769945344]: GUI: Scanning Single Parents Season 1 Episode 2
2018-11-08 16:22:25,781 - INFO - UTILS [140252769945344]: GUI: Scanning Single Parents Season 1 Episode 3
2018-11-08 16:22:25,782 - INFO - UTILS [140252769945344]: GUI: Scanning Single Parents Season 1 Episode 4
2018-11-08 16:22:25,783 - INFO - UTILS [140252769945344]: GUI: Scanning Single Parents Season 1 Episode 5
2018-11-08 16:22:25,784 - INFO - UTILS [140252769945344]: GUI: Scanning Single Parents Season 1 Episode 6
2018-11-08 16:22:25,785 - INFO - UTILS [140252769945344]: GUI: Scanning Single Parents Season 1 Episode 7
2018-11-08 16:22:26,526 - INFO - UTILS [140252769945344]: GUI: Requesting metadata for 'Single Parents'
2018-11-08 16:22:26,541 - INFO - UTILS [140252769945344]: GUI: Background media analysis on Single Parents S01 E07
2018-11-08 16:22:27,085 - INFO - PLEX [140252769945344]: Finished scan!
Always go pretty fast.