It's a noisy little engine.4 Valves clacking & a cam chain whizzing along its giudes. 15,000 miles isnt sucha big deal. It's getting about time to have a peek at the tensioner & see where it's sitting. Some guys get good long service outta the cam chain, others, not so good. The tensioner has no "stop" on it & can come apart & send the spring sproingin into gears & create havoc. I don't want to be an alarmist, but the dang thing can sure bite ya.If it was mine I would just have to look in there. You might get a pleasant surprise & your adjuster only be out 12 or 14 mm, or, it might not be so cool.