Some people have actually removed the clutch helper spring from their clutch pedal so as to get a "better" feel of when the clutch grabs, and don't mind the extra effort to push the pedal down. See thread below. I guess it is possible that the previous owner removed theirs, or that it has worn down, and needs replacement (some people replace as well, and claim it helps). If this isn't it, it could just be that the clutch is getting worn, but I've noticed my clutch being heavy all the time. I've driven friends' Boxsters too, and it varies...some are heavy, some light. Not sure why there's a difference to be honest, but none of them felt so heavy that it becomes a nuisance.
https://www.renntech.org/forums/topic/13367-clutch-booster-spring-removal/