Three hypos in one night, that is not fun. I'd ask a couple of questions:
What were the basal rates on your pump like?
Have you tried fasting during the day and seeing what happens to your bgl?
Does this happen every night?
Is there something else, exercise/food/novorapid that could be causing the hypos?
If you want I'd chat to your endo about it. Whenever I've switched from a pump to Lantus or vice-versa it's never smooth.
Just for good basal coverage and having to be less finicky about injection times I had a lot of success splitting Lantus doses. For me Lantus never made it the full 24 hours it was more like 18.
As for the lows... When I was on Lantus this always happened to me. Turned out I was on far too much of it. If I didn't eat for more than 3-5 hours I'd go low.
So, my guess is you're on too much Lantus -- even though 15u seems like a small dose. I don't see how splitting the dose is going to help that much with this. You could try having a larger dose in the morning and a smaller dose in the evening to ensure that the minimum effectiveness of Lantus occurs in the early morning. Or you could try a single injection in the morning for the same result. But you might go high in the morning... From memory my Lantus split was roughly 65%/35% am/pm.
Another option would be to switch to levemir and take a larger morning dose and a lower evening dose which hopefully would lower the basal insulin effectiveness even more than an uneven split with Lantus.
Also a bit of a crazy suggestion -- if a lower dosage of Lantus gives stable overnight bgls but high bgls during the day you could try using a small injection of Levemir or NPH in the morning to give a bit more basal insulin during the day.
tldr: Looks like too much lantus overall. Aside from lowering the dose I'd try a different injection time. And if it were me I'd split the injection just for coverage.
If you decide to lower the dose to titrate Lantus down I go down by no more than 10% every three days. Maybe overly cautious but I've never been DKA and never want to be.
Sorry for the long post. I hope it helps and best of luck. Constant lows are the worst.