Yes, 1800 files in Quarantine matters. Typically most servers will only allow you to delete up to 300-500 quarantined files at one time max. If you have BPS Pro 8.3 installed then use the Sort/Search feature to delete files by sorting them first.
“As of BPS Pro 8.3 a new Quarantine Sort/Search feature has been added to Quarantine that allows you to sort files by plugin folder name or theme folder name. If the total number of files in Quarantine exceeds 200…”