Long delay to show CopyQ notification when copying 0.5MB of text to clipboard

**Describe the bug**
When copying 0.5MB of text to the clipboard there is a long 10-20 second delay (depending on processor speed) to display the CopyQ notification.

**To Reproduce**
Steps to reproduce the behavior:
1. Open any text editor
2. Create a 500KB (0.5MB) text file
3. Copy the contents of the text file to the clipboard
4. Notice that it takes CopyQ 10-20 seconds to respond with its notification

**Expected behavior**
The notification to appear momentarily after the copy operation is performed.

**Screenshots**
N/A

**Version, OS and Environment**
(From `copyq version`)
- CopyQ Clipboard Manager v3.13.0
- Qt: 5.13.2
- Compiler: GCC
- Arch: i386-little_endian-ilp32
- OS: Windows 7 SP 1 (6.1)

**Additional context**
I experimented quite a bit turning off different CopyQ settings/features that I thought may be increasing the delay, but nothing I changed resulting in the notification displaying quickly after the copy operation was performed.