Oil fouled spark plugs are pretty normal for 2-stroke engines, especially snowmobiles that get run for a bit then shut off during the summer months. You will find most guys change the plugs at least once a year, and always carry spares.
115 compression is not too bad, anything above 100 will run the engine. As long as the engine starts easily and has adequate power, I wouldn't be too concerned. With less than 120 compression, the rings may be showing a bit of wear, but not bad enough to require replacement.