Ignoring the issue of particular enriched air mix and depth combination - you later amended that, and it wasn't the focus of your question anyway, even if it did generate a lot of comment - there is really no reason to fundamentally change your (presumed) previous plans for a normal ascent, just because you are ascending on air instead of enriched air. You have plenty of gas (30cf) to ascend from 130', and the fact that you are breathing air instead of a slightly enriched mix on the ascent is inconsequential, in terms of the actual additional nitrogen loading that would occur during the ascent. You could use the schedule you proposed. Or, you could ascend at your normal rate (let's assume 30 ft/min) to your 15ft S/S (or 20ft, if that is your preference) and hang out there.
What would I do if my backgas became unavailable at 130', and I had a 30cf bottle of air, and was within NDL? I would ascend normally to 15ft, do my safety stop, and surface. If I wanted to be very conservative, I would add 5 min to my S/S. If my backgas becomes compromised, and I have a more limited reserve (e.g. a 13 cf bottle, instead of a 30), my interest would be in getting shallow sooner rather than later - but, again using a safe, normal ascent rate - and doing whatever safety stop I could with the remaining gas. If, for whatever strange reason, my limited reserve ran out (bottle wasn't full to start with, I was breathing hard looking at the tips of the trident sticking out of my tanks, I was using a Spare Air, etc) I could more easily do a CESA and surface from 15 ft than from 70 ft.
