Can I use a fresh peach in place of preserves?
Preserves are pretty sweet and thick. They're also usually chunky; jam is closer to a puree. If it's just in a marinade that'll get thrown out, texture probably doesn't matter much, but if it's part of a sauce for the pork chop, the chunks can be pretty nice.

The closest approximation would probably be to dice your peach, add 1/4 to 1/2 cup of sugar, and cook it for 5-10 minutes in a saucepan to get it to soften up and get juicy and flavorful.

As a slower but simpler to cooking you could just let it sit for maybe half an hour to macerate; while that won't be quite like preserves, it'll also release some flavors. And if it's for a marinade, that could be part of the marination time, though you might want to give it a stir once or twice. Just using it raw and pureed might not be quite as flavorful, though.