Hi and welcome to the forum.
Whereas you can ‘update’ either or both cameras this does not update the phone to an FP3+ This is because there is a slight difference in the core module which you see via settings @IkarusFP3
With the FP3 no matter if you change the cameras you will still see Hardware version Fairphone 3, not Fairphone 3+ as in the screenshot below
Settings > About Phone > Model see screenshot . . .
There are other more or less insignificant issue like the back cover plastic quality . . .
You may/will notice that the settings on the front camera only show 4Mpx not the 16Mpx if you choose to upgrade that one and I’m not sure for the ‘selfie’ camera a change from ?MPx to 16Mpx is going to change that much.
The rear camera although having more Photosites at 48MPs only provides 12MPx shots.
There’s no change in that respect, but you can with any camera change the app. which can offer different settings etc.
The delay is often due to the use of HDR which means their is a processing before you hear the ‘click’ etc. and even more delay whilst the images are merged etc. for saving.
You may like to look at Open Camera and Nikita as alternative apps to the default camera.
You can read about them here if you search, I’ll see if I can find some useful posts and update here. Looks like @urs_lesse has just done that.
All the best
See also