engine maintenance

Hi! I'm new here and I'm wondering if anyone here is familiar with Rotax915? I'm looking at one aircraft that's powered by Rotax915 and upon reviewing the cost of maintenance, I notice that the seller states that the engine requires replacement every 1500 hours. I'd like to know if anyone who is...

Sometimes the time saved flying at 75% power outweighs the potential gas saved by flying at 55% power. So why not fly at 75% power all the time? My question is, in terms of overall engine health, is it better to fly at 55% power? Or is it better to fly half a cross country flight at 55% and the...