It probably depends on your swimming background. I did my HIM with only swimming about once every two weeks - won the swim in my division too. But the mile was my swim event in college, which was awhile ago, (yowza! more than 20 years!) but I don't think your body totally forgets. I'm lucky to have lots of upper body strength naturally too.

The sprint swim distance seems to vary. It seems to me that if you are swimming twice a week and doing the same or more distance than your event, you can complete the event. Maybe not fast, but you can complete it. But I'm not a coach, only know what I did.

Veronica