Hi & welcome

Glad to hear you've found the site useful so far & have decided to join. Another new recruit, yay!
Firstly, losing 16lbs in 2 weeks is likely to be primarily water weight, not fat. That sort of loss is not something which could keep going at that rate and I imagine the methods used to lose it are not the sort you would want to do in the long term. Plus, think of all the nasty loose skin you'd end up with if the weight loss was so rapid and kept going like that!
A sensible, healthy rate of weight loss is by most health professionals' standards around 1lb a week of loss as I'm sure you know.
Now, on 5:2, as you'll see from the Progress Tracker if you sign up, most folks do have a greater loss in the first few weeks, which then slows down. I think most of us who have a fair amount of weight to lose (ie, a couple of stone or more) find that the first stone comes off in around 4-6 weeks. After that the losses may slow somewhat to a more steady 1lb a week, some users find it's more, a few find it's a bit less.
The great thing about this way of eating is that it doesn't leave you feeling deprived like so many other diets do. It also sort of resets the way you think about food and hunger - really quite empowering!
I've tried general calorie reduction so many times in the past, only to regain all the weight because I can't keep going without my high cal treats like chocolate, crisps, takeaways etc for the long term. We shouldn't have to if we enjoy our food.
So, two days a week I eat 500 calories - I'm not generally hungry during those days and have a huge dinner for those calories with plenty of veg and some filling protein. The rest of the week, I eat as I normally would - which includes things like biccies, chocs, takeaways etc. That said, I don't feel like snacking as often as I used to and for the most part I actually find myself wanting more healthy foods. My meals are generally very healthy but I'm not deprived in terms of the foods which many diets forbid.
Please do feel free to ask any questions you may have and we'll do our best to answer. I hope this explains a little of why 5:2 is so great. No, it's not a quick fix - but it's a way to lose weight and keep it off in the long term!