MacBook Pro a lot slower after reset
I had this issue recently, and I realized I had incorrectly reset the NVRAM. I simply went through the reset again, and all was well. It's fairly easy to do. You just need 6 fingers on each hand.. Here's the Apple site explaining how to perform the reset. Here are the salient points (but I urge you to read the article).

On Mac notebooks with non-removable battery:

Mac notebook computers that have a battery you should not remove include: MacBook Pro (Early 2009) and later, all models of MacBook Air, MacBook (Late 2009), and MacBook (Retina, 12-inch, Early 2015).

To reset the SMC:

Shut down the computer.

Plug in the MagSafe or USB-C power adapter to a power source and to your computer.

On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time. (note, not the Command key!).

Release all the keys and the power button at the same time.

Press the power button to turn on the computer.

On MagSafe power adapters, the LED might change states or temporarily turn off when you reset the SMC.

On Mac notebooks with removable battery

Older MacBook and MacBook Pro computers have removable batteries. Learn about removing the battery on MacBook and MacBook Pro.

To reset the SMC:

Shut down the computer.

Disconnect the MagSafe power adapter from the computer if it's connected.

Remove the battery.

Press and hold the power button for five seconds.

Release the power button.

Reconnect the battery and MagSafe power adapter.

Press the power button to turn on the computer.

Hope this helps.

It's worth a try before heading the dealership..