if a client website is very slow i will follow a structured approach to debug.
- i will check plugins either we are using too much plugins
- Either plugins are updated or not
- Either theme we are using is light weight or updated
- i will check images like the images are optimized or not they are in the correct format or not
- i will check the cache plugin either website contain cache plugin if not i will install
- if the website is too large i will check the hosting plan we are using either it is up to the mark or not.
- i will check through query monitor i will delete the post revisions this approach will boost up website speed.