I assume you are referring to the rotational speed of the disk when operating in random orbit mode. (not to be confused with the motor speed, which would be a completely different situation.)
Yes, the disk should be rotating at a reasonably high speed to give you the best random-orbit effect. Of course the most frequent cause of a slow rotational speed is pressing down too hard. That should be avoided. However, it may also be that your pad brake is being too effective. Normally there is a small amount of dust between the pad brake and the pad backing, and this acts like a lubricant to keep the pad brake from being too aggressive. On a brand new sander, there should actually be a small amount of grease-like lubricant on the back of the pad for this same purpose. So if your sander is very clean and dust-free, you may want to add a small amount of any lubricant to the back of the pad between the pad and the brake.
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