I had recently upgraded another system (MBP) and noticed it was a little sluggish.. It was spotlight working hard to do its job.. But I didn't need it to do so on an external drive. Using this method was the key!
If you turn off the Mac and turn back on, then go immediately into system prefernces (via the apple icon top left) the spot light preferences are in there - you need to be quick before it starts to index them.
If you search turn off spotlight index in google it will come up with more detailed info