15 years of marriage and 'his transport issues are not my problem'?
You live really close to work, it's summertime, and the walking will do you good, you can skip the gym. Maybe he can drop you off/ pick you up some of the days.
I had car issues once. My ex would wake up at 6am to drive me for 45 mins for almost 2 months. Separate finances, for context. And 10+ years. I didn't ask him at all, but had he been able to but not offered, subconsciously it would have made me resent him. I'd have done the same for him.
Heck, even my friends would do this for me, and I'd do it for them. Another time I had car problems, my friend had me stay with her, at no cost, for a week. Another time another friend just drove me home for several weeks...
Do you love this person? If so, do you not have the innate desire to look after him and help him have a comfortable life, and not spend $$$ on a hire car that could go towards, I dunno, the children, or nice days out for you both?
Romance is dead if one won't go out of their way to help their nearest and dearest.