The only way you can really know is to get the oil tested.
I have been running synthetic in the truck and tractor for years and testing the oil. The oil in the truck will be changed out in a year due to use. The tractor has gone at least two years and the test said I threw away perfectly good oil. The only way you will know is to test.
The cheapest thing to do is to use the cheapest oil that meets the engine requirements and change per the manual. I like know what is happening in the engine so I test the oil and I like to use synthetics for a variety of reasons. Testing and using synthetics cost me a bit more, maybe, but I run longer on the oil.
I have only had three oil samples that were iffy. Two samples, one in the truck and one in the tractor, showed a bit of fuel. Nothing bad but the fuel should not have been there. Why? I was running the RPMs a bit too low on the tractor. I seldom mow and thus I don't use RPM speed but a few times a year. A the time I was running 1500-1600 RPMs just doing this and that on the tractor. After the sample, I pushed up the RPMs to 1800-2000 and no more fuel in the oil. The sample in the truck was because of getting in quite a bit of stop and go traffic. I would spend maybe 15 minutes stuck in traffic out of a 60 minute trip but that was enough to let in the fuel. Thankfully I was able to avoid that route otherwise I would have had to change out the oil sooner.
The last truck sample had a more wear than usual. Not an amount that is immediately alarming but something to watch. I think it was because I let the oil get a bit low but time will tell. Without testing I would not know.
Later,
Dan