A tried and true test way of speeding up mail via pop into your gmail is to:
- At the top right, click the gear (cog) Settings.
- Select the 'See all settings' button.
- Select the 'Accounts and Import' tab.
- Scroll down to the "Check mail from other accounts:" section and click "check now"
Google claims that to refresh POP accounts you can click the refresh link at the top of your inbox, but we havnt found that to be the case and instead suggest the first method above.
https://gsuiteupdates.googleblog.com/2012/08/three-gmail-labs-graduation-into.html