Sliding on your back for 15’ on asphalt must be an interesting experience. Probably will feel like a blistering sunburn for 2 months.
And repeatedly cracks open while healing.
A few decades ago I was a regional champion and nationally ranked bicycle racer. I have slid on the pavement a lot further than that. Typically, you end up with a some road rash which like you say is similar to a sunburn, but with some deep scratches or worse from gravel or debris on the surface of the pavement. The courseness of the surface also can make a big difference. But if you are very active and are able to ignore discomfort... it usually does not slow you down much and gets better within a week or two depending on how deep your wounds are and if you are able to get them completely cleaned out.
I can remember getting up and picking decent sized pieces of gravel out of my skin. I still have a one inch diameter scar from a piece of gravel that is just to the side of my elbow where I slid about 50 feet across a couple lanes. The furthest I ever slid was in the winter when I hit a patch of ice in the morning, but my winter clothing protected my skin and I was still able to go on an 80 mile bike ride with just a little extra ventilation in my clothing.
These days I can end up with worse pains from activities where I don't even know what I did.