Cambelt was done in 2019 on the black one which is good.
Yes that is essential so good news.
I would still think about the white 2015 plate its going to hold its value slightly better & has lower mileage. Get test drives on both to see how smooth the clutch & gearboxes are. Closely examine the bodywork look for signs of any accident damage repaired (lower sills under the doors have a factory stipple finish this is normal its to reduce stone chips issues. Renault & other French manufacturers use this method on recentish cars).
Also ask about track useage as brake discs & pads wear out faster so might need replacing if they have been used heavily on track days!
Engine bay as well check to see how clean & look for oil leaks on the floor sometimes the camcovers leak oil due to faulty gaskets (many owners do not even notice this) its cheap to fix but something to be aware of.
If either car has had a racechip or fuel injection turbo timing mod or tuning box I would avoid (you would have to tell the insurance company it would double the quote!). The engines are bulletproof & really strong as standard but easy to install undetectable ECU mods add another 50-75BHP & 70-80NM so expensive to replace components will wear out faster if not driven with care! These F4RT (yes that is the real Renault code for the engine!) RS engines are really strong & so is the gearbox but if an owner has started to extreme tune you need to be careful.
Another option is look at the RS250-265 from 2010-2013 always plenty around going for £6-7K leaves you plenty of money to address any issues if they come up. In real world road driving you would notice zero difference between RS250/260/275 (apart from fuel consumption!). The entire Megane RS range from 2009-2013 uses the same F4RT engine (newer have slightly more turbo boost pressure & larger intercoolers & ECU tweaks) all are capable of giving out more or less the same power as no changes were made to the actual engine internals they all use the exact same pistons, cranks, cylinder heads, same gearboxes & clutches etc etc. Only Mk4 onwards are totally different but way more expensive.