I have Lightroom 6 (CC) and since the last update, it runs so slowly it is completely unusable. I have a Toshiba Qosmio, W7(64bit) Home Premium, 8gb ram, NVidia GeForce 560m. I've never had any issue running any other version of Lr, Ps, Br. This started with the last update.
Try turning off the Face Detection feature
It isn't on
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I have the same issue. iMac 27" Retina. Face detection, location and synch turned off. Turning GPU on o roff makes not difference. It's taking up to 30 minutes to swat between a smart collection with 5 images to 1 with 7. It must be something I am doing wrong as it's totally unusable.