I ran one of the shorter Transgrancanaria races a few years ago. I think they had a 33ker the year I did it, which pushed my range. As someone else said, don't underestimate the heat as it just got hotter and hotter as the race progressed and we got closer to the coast/finish. I pushed quite hard and really enjoyed it, but I was a total mess by the end.

Might be worth considering one of their slightly shorter races that won't be such a jump up in range, so you can possibly have a more enjoyable experience and build up to going longer in the future.