Is Dynamics CRM slow?

At work, we have an on-prem version of Dynamics CRM 2016. It is common for a page to take 5 seconds or more to load on the Dynamics CRM website. 

Is this normal for Dynamics CRM 365 or is there performance issues with custom made plugins which are used?

I am asking because I am just curious if Dynamics CRM is a slow product or if it is slow because of custom plugins or internet connections.

Thanks in advance!