Not quite.
As mdpe comes out if the floor, replace the current brass stopcock with a 25mm elbow mdpe pointing to your 15mm copper and use the reducing set to attach the copper to the elbow.
Then... Cut in a 15mm lever valve on the 15mm copper.
You don't need the additional adaptor, the...
IME, if your main is copper from street to house then adandon it.
It will likely be failing in several places and as each leak is repaired, the increase in pressure will find the next weak spot.
Get your insurers to look at moling a new main and going into the house as near to the internal...
Get a 25mm mdpe elbow.
A reducing set to replace the 25mm collet and O ring in that elbow.
Stick a bit of 15mm copper into it.
Put in a lever valve (making sure you'll be able to operate it when it's below/inside the Kitchen unit when it's fitted) and then onto the 15mm house supply you have there.
Are you sure it's not condensation on the pipe?
I'd rather have soldered joints on anything before the internal stopcock and defo no Ballofix.
Change the stopcock to a lever valve.
When I say meter... I mean "their kit"!
With that mains burst photo you posted, all sorts of debris would have got shoved downstream and likely fouled up loads of filters/NRVs at the meters.
FFS!
It was the suppliers meter end of.
And then they send a femgineer who's sole purpose is to prove she's got bigger Bollöx than a man.
Equality my arse!