No,,it's more like filling past a certain amount (%) will slow it.Is a SSD like a HDD where the more you fill it up the slower it becomes?
If you fill a hard disk drive more than 85% full you cannot defragment it. I defragment my hard drive almost everyday. Yes I know it is excessive, but I love having a fast hard drive.
Speaking of, you do not need to defragment your SSD. It'll be the same speed and actually cause more read/write operations.