£15k doesn’t sound all that much if fairly major building work involved too. make sure you have a contingency fund for unseen problems.
I also fit kitchens for a living, I reckon our average job price this year is £25k. max being £54k!!!
Spend a good long time on the design to make sure everything works before committing, I’d look for drawers for base units rather than cupboards, they make access much easier. Good quality but not OTT appliances, I personally like Siemens at the moment, rather than Miele, especially for the budget. 2nd the induction hob, I love ours but make sure you have the juice to run it.
I prefer ovens and fridges in towers if poss but that’s personal preference.
Silestone worktops are our current most popular, but are approx £350/m which is still a lot cheaper than Corian.
My favourite kitchen gadget is my Quooker, saves a lot of time and faff but you’d be struggling to justify one on cost alone.