09-23-2015, 03:30 PM
4GB of RAM is not helping the situation. There's a diagnostic tool called EtreCheck that can sometimes point you toward bottlenecks: remnants of MacKeeper, bad antivirus software, etc. Worth a try. If the owner has ever downloaded software from the likes of cnet or softonic, or from torrents, there could be malware or crapware installed. But the skimpy RAM and possibly not having enough free HD space could certainly be the culprit. Regardless of Apple's system requirements, 4GB is not enough for Yosemite to run well. Plenty of reports along those lines in Apple Discusssions.