Back when I had a proper job (as opposed to spending every day doing things I enjoy!!) I used to commute 12 miles each way over Sheffield hills, virtually all off road. Hills, sheep tracks, moors, woods, even a ford. I wasn't fit, not at that level, but I kept at it, starting at one or two days a week, and increasing as I could. It wasn't an easy task, I was out on my bike at 6:45am with a long, slow slog up hill, about 800 feet of climb, and in winter, of course, in the dark. When i began, I was told it would take two years to adapt to it. After six months, I thought I'd cracked it, cycling most days and most of the year round. But after two years, realized it had changed, now cycling every day, even at minus ten degrees, in snow, in everything but snow on top of ice, without worrying about the hillsor the weather. It was by then the best part of my day, it inspired me to far better things than the career I had at the time.
I had shower facilities there, and a canteen for a cooked breakfast. I'd roll up at work at eight am, having cycling through a glorious moor top sunrise, been down through the woods, cycled through the city parks, had a nice shower, got changed into office clothes, and had breakfast. My colleagues would be turning up by then, frazzled by rush hour traffic and nowhere to park, or sneezing from city in their office clothes on a steamy bus, after waiting for it in the rain. I could never understand why it was them that thought me mad, rather than the other way around!!
So, 16 road miles is do-able, more than do-able, and to whom does it matter how fast you do it???