Skin food mask- steam with wet flannel (reminder not the best for the sensitive skinned among us) then apply thin layer of skin food and leave for 10 mins, then wash off with warm flannel. I've used it as a thin sleeping pack too but that's really in an emergency only.
I tend to go by the rule of always buy skincare you can afford to use down to the boob area, if you're using it frugally on the face only you really can't afford it. Neck area is often neglected and the first thing to age because of it.
I'm not familiar with C15 booster, (they can't sell anything over 10% Vit C here, I can't seem to find it on the UK website either, can you link?). The first reviews that are coming in say the PC Niacinamide is somewhat better than the Ordinary Nia but enough to justify the price discrepancy. I only really like PC for her BHA, the rest contains a lot of silicones and in recent times it's moving very much away from its original ethos of transparent universal skincare at affordable prices (the company's been sold twice now, prices are rapidly increasing with a very clear for profit model, PB used to bash Asian Beauty now all the new products seem to be inspired by it) not to mention the many issues I have with their PR/bashing of other brands by measuring it against their own model. If there was a better BHA or even just as good out there at a higher price I'd be buying that purely on the back of their business m.o.
If I was going to be spending serious money on Vit C (which I find really really hard since it's so cheap to make and usually oxides before you finish it) I'd go for the Skinceuticals one (I was halfway to buying samples, 5/6 little bottles that equate to a full bottle for around $50 USD (shipped) from ebay from a reputed reliable seller with fresh batches before the Ordinary showed up) or I'd get the NuFountain one from Amazon.com that's made fresh and pretty close in formulation to SC. Obagi is another possibility but they have various ones (some sold only in Derm offices) and I'm not a huge fan of what else they're putting in there at that price point.
I saw that email too, Aurora, all the silicones and the nonsense about plant 'stem' cells really put me off as well as their allusion to cell communicating ingredients... ugh, lost a bit of respect for NIOD.