Looking for a laptop

Been looking at laptops, and I see some cheap laptops have Celeron and Pentium processors, how do the compare in performance to i3 and i5 processors.

Would like a 15 inch laptop, preference is hp because the build quality looks good but open to suggestions.

I don't know a thing about a "computer".
It was only 6+ years ago when I bought my 1st computer. I learned how to use it by trial and error and asking questions in the newsgroup.
So I won't even try to make recommendation.
However, I would suggest that you offer more than just the screen size as preference.
For instance....................
How do you plan to use it , for home use or for business ?
A gamer computer ?
Price range ?

Details in preference will give others an idea which model is best for you.

It's for home use, mainly email and browsing with the odd document. Battery life is of interest so I can take it downstairs for the day and use my desktop in the evening. My desktop has a core 2duo e8400 and crucial ssd which is plenty fast so looking for a laptop to match this in speed don't know what the current equivalent to my e8400 @ 3.0 ghz.

I can use my tv to browse the internet bit would prefer a laptop with WiFi instead that is as fast as my desktop with good battery life and decent sized screen, btw I am in UK.

Here's one place to start for an overview:

It's for home use, mainly email and browsing with the odd document. Battery life is of interest so I can take it downstairs for the day and use my desktop in the evening. My desktop has a core 2duo e8400 and crucial ssd which is plenty fast so looking for a laptop to match this in speed don't know what the current equivalent to my e8400 @ 3.0 ghz.

I can use my tv to browse the internet bit would prefer a laptop with WiFi instead that is as fast as my desktop with good battery life and decent sized screen, btw I am in UK.

Seldom do Notebooks have more than 4 to 5 hours battery time and that decreases as it gets older.

I have several Notebooks and a Tablet and the best battery life is with my Dell Venue 8 8" Tablet that came with Win8.1 but now has Win10, usually a bit over 6 hours.

It's for home use, mainly email and browsing with the odd document. Battery life is of interest so I can take it downstairs for the day and use my desktop in the evening. My desktop has a core 2duo e8400 and crucial ssd which is plenty fast so looking for a laptop to match this in speed don't know what the current equivalent to my e8400 @ 3.0 ghz.

I can use my tv to browse the internet bit would prefer a laptop with WiFi instead that is as fast as my desktop with good battery life and decent sized screen, btw I am in UK.

You don't need much power for your CPU, Corei3-5005u will be fine, I have recently bought a Lenovo G50-80 for my daughter, it has 4GB RAM, i3-5005u, 1TB HDD, it has a very good screen but you should visit a store and check for yourself.
Acer Aspire E5-574 is another good laptop. Whichever you get, replace the hard drive with a SSD.

Will look at those two, is the SsD difficult to fit?

Will look at those two, is the SsD difficult to fit?

In Lenovo there's a service hatch and need to remove 3 screws and it's easy, in Acer the whole back cover has to be removed but there will be a cable connected and I'm sure that you can manage with few videos in YouTube.

Cheers, need to search these two models out.

No problem and good luck.