WordPress super slow on Client's computer!

I recently have a client who is complaining that their WordPress is very slow.

On my computer their WordPress backend seams to be running quite quickly.

I fear this might have something to do with a blocked port, or maybe a firewall on their internet connection. I tested their internet out on my laptop and I still had the same problem. Internet connections play role of their speed, but you’d think that most modern internet connections would support a WordPress backend login.

I am a little unsure what to advice the client. They live in a rural area (England), so this might have something to do with it. Has anybody experience a similar issue with any of their WordPress sites?

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