Hey OP,
I don't see why a baby would be so disruptive. Presumably your eldest has their own room to study if they need peace and quiet (even if they don't you'd have baby with you presumably the first 6-12 months). Life doesn't go on hold just because you have exams this year.
I think the real question is :
- Do you want a baby enough to start over again ?
- Do you have the means to deal with the logistics (costs, space, planning, etc)
If the answer to both of these is yes, go for it.
If it's no, or not sure, then think about it a bit more.
The advantage of the large age gap is that your eldest will be very independant so it'll be much easier than if they were, say, eight, old enough to have completely different needs from the baby but young enough that they still need you a lot.
This said, if you go for it I'd try and be careful to check in with the eldest regularly to make sure their needs are met and they're not pushed aside for the baby.