I agree with engineer54 , i have done an installation of this size and had to split lighting into 4 lighting circuits, 4 socket circuits, 3 ensuite showers , ya 15 way will not allow 15 MCB's will generally allow 7 + 6 with RCB kit to create two RCB/RCCB buzz bars...which is a requirement as said above to allow user to find their way to CU if one RCD/RCCB goes.
two 10 way CIU's can sometimes be cheaper, i get 12 ways (6+6) inc choice of MCB's for £50 , but a 15 way from same supplier is £110 inc second RCD then extra for and individual MCB's.
but you are right to question first fix, current 17th has a large emphasis on installation method, and without installing self you cannot be shure they are not burried in insulation. (upto 50% reduction in current carrying cappacity) just waiting for a fire.
second , my experience of decorators is they over do everything pull on cables, and thus reduce the CSA (cross sectional area) of a conductor. again reduce current carrying capacity... and will not necessarily show up on continuity test (second fix testing the electrician will do ) ..as long as the ohms reading is small enough it passes. but you get a hot spot ...and this hot spot 9 times out of 10 is where its a tight fit in a joist in bundle... again fire waiting to happen. and sods law being applied, they will shove some insulation in there to make it worse. just and example of how important a suitably qualified person should supervise or being doing first fix.
probably too late to help but others may appreciate
